Greetings you unhappy vikings who missed (or disliked) pre-order but still wanna play with that insane dude, Tryggvi! Your days of anguish for lost-love, brooding over your mug-of-mead and general boredom are over. Behold! The modding community has found multiple ways for you to easily "activate/unlock" that playable character
First of all, thanks are due to the developers for keeping the game so "open" to modding and, specifically to the technical director, the one and only, John Watson, for supplying tons of information & dev-tools that help the modding community's march to glory.
So, without getting into too much details, all that is needed for Tryggvi to appear in Skogr (Chapter 2) is a global variable of the game, called "tryggviunlocked", to be set to "true" (or numerical value 1). This is by default set to "false" (0), unless you have pre-ordered. Here is not one, not two, but three ways for you to unlock Tryggvi. Choose the one you feel more comfortable with and...
ATTENTION: I recently noticed that following one of the last patches that reworked the file-structure and the game-console, only Method#3 works as described in my post, below. Methods #1 and #2 also work, but slightly differently; refer to YaK's post for the how-to. Checked for TBS1 Build v2.18.08 (Steam) at Jan-2016
DISCLAIMER: Do this at your own risk!
 Editing your save-game file with a normal text-editor
This will make Tryggvi appear only for that specific play-through you're actually playing. Once activated, he'll stick along your journey; but, if you restart a fresh game, he won't appear. So, while you are in-game, and after you arrive in Skogr and inform Iver about the incoming Dredge, and before you get into that first battle in the village by clicking on the Skogr HOUSES, stop & quit the game. A save game on that game-point will be generated in your save folder
- Mac OS X: ~/Library/Application Support/TheBannerSaga/Local Store/logs/saga1/resume.save.json
- Windows: %HOMEPATH%\AppData\Roaming\TheBannerSaga\Local Store\logs\saga1\resume.save.json
Locate that "resume" save-file and open it with a standard text-editor (e.g. WordPad or notepad++ in Windows). Search for the string "globalVars" (about midway down the bottom), where you'll find a list of all the game's global variables that have been changed from the default values for the current play-through.
Add the entry in the appropriate alphabetical location, i.e. the lines in red from the code below reading:
Save the file, launch the game and load the "Resume" save file. Click on HOUSES, and the mustached hero should appear
 By using the dev-mode console to set a global variable
This will make Tryggvi appear only for that specific play-through you're actually playing. Once activated, he'll stick along your journey; but, if you restart a fresh game, he won't appear. To activate the dev-mode console, add the handle developer in the game's launch options:
So, launch the game as you would, start playing and, at the exact same point that was pin-pointed in the previous section of this post, stop & activate the console by hitting
on your keyboard. The game's window will be overlayed by a bunch of text, with a green line and a prompt in the bottom. Hit
Steam > Library > R-Click on TBS icon > Properties > Set Launch Options > developer
(and return) and exit the console using the same key combination as before. Click on HOUSES, and the mustached hero should appear
saga set tryggviunlocked 1
 By modding the game's "master file"
This will permanently activate Tryggvi for all fresh play-throughs you start; however, it will not affect old save-games. Here, we're gonna be editing the "master file" of the game, where all the vital information is stored. Each time a new game is launched, this "master file" is invoked to initialize all variables. So, we will manually "set" the starting value of the tryggvi-controlling global variable to the desired value. We are gonna need the JSON-decompiler tool supplied by John (check these posts to download it). So, launch this program and open the file:
(that is where the game's files --not user files-- are installed in a Windows system) and add the line in red from the code below:
Mind the comma after "tryggviunlocked"! That part of the code is near the bottom of the "monster/master file", in line 5951 of 6493, approximately. Save the file (a backup of the original is automatically generated, with the .ORIG extension) and launch the game. Start a new fresh game, and once your reach Skogr, the mustached hero should appear
If you're not comfortable with editing (or lazy!) -- You can download the modded-file I made here (link removed, cuz file outdated), and just copy/overwrite the one in your game files (don't forget to make a backup of the original before you overwrite it!). ΑΤΤΕΝΤΙΟΝ -- That file in the URL was tested and found to work fine with the latest version of the game (TBS1/Patch 2/v2.6.45 as of 27-Nov-2014) on my system, but I am not sure if there's any more edits in there not related to unlocking Tryggvi; it's unlikely that those will break your game, but in any case, I advise you do the editing yourselves!
That was it! Easy, no? Now take back all the grief aimed at the devs for pre-order exclusives, as they kindly let all this practically open for anyone to meddle with, and they supplied all the info & tools needed to do the meddling-with!
PS1 -- Please report any problems with the above "solutions".
PS2 -- Note: I've devised & tried the solutions on a Windows7 Steam version of the game. I am sure something similar will work for the DRM-free (GoG) versions of the game.
PS3 -- For those in the GoG version: A fellow member, Yak, confirmed that the console and the methods described work similarly.
EDIT #1 -- Method #3 is not working as intended... Looking into it...
EDIT #2 -- OK. Fixed Method #3. Actually, it is much simpler and elegantly done, this time... I wonder why I didn't notice it before! Thanks for the feedback, Yak
EDIT #3 -- I highlighted that the modded-file-for-download (Method #3) might not work for future patches.
EDIT #4 -- Updated URL for the modded saga1.json.z
EDIT #5 -- Added a notification that only Method#3 works [23-Jan-2016, v2.18.08]
EDIT #6 -- OK, YaK just verified that Methods #1 and #2 also work, but not as I described. Check his post (#40) for details [31-Jan-2016]
EDIT #7 -- Removed link to pre-edited Saga1.json.z file, because it was outdated [9-May-2016]