So I went through and saw some neat videos on youtube of people replacing characters in mass effect but I couldnt come across any easy to use instructions for people so I figured I would post some. These instructions are for the pc version of the game.
1) Download and install a copy of notepad ++ (you can get it here) It's not really a requirement, but it tends to add extra bits into files less often. If you can't or won't install it you can use regular notepad from windows but DONT USE WORDPAD. It may insert extra formatting into the files and screw them up.
2) To replace shepard with another character like tali or garrus (or any of the party members with any other party member) we will need to look at the biogame file. So open windows explorer and navigate to where mass effect has stored your saves and configurations. Typically this is in your my documents folder.
In your my documents folder navigate to the bioware folder, then the mass effect folder, then the config folder.
If you make it to the correct plase you should see a handful of .ini files. The file we are interested in is BIOGame.ini (MAKE A COPY OF ANY FILES YOU EDIT BEFORE PROCEEDING) so right click it and hit edit with notepad ++ (or just regular notepad if you skipped step 1)
3) Now we need to tell the game that instead of loading shepard's character model we want it to load garrus.
You will see that the file is divided into sections followed by the entries for the sections. Scroll down until you see the section named "BIOC_Base.BioEvtSysTrackVOElementsInst" Rolls off the tounge doesn't it? More importantly this is where the entries for party members are located. Looking through the entries you should see a line with lots of the species of character that you want to use. In our case we want to replace shepard with garrus so we are looking for turian.
That fits the bill. But we dont need the whole thing, only the Actor type is important for what we are trying to accomplish so the important part from our line is:
Thats the portion of the line that specifies what type of character to load, as well as what meshes and textures to use.
So copy that portion of the line and start looking for the portion of the file that specifies what shepard looks like. So scroll up and look for the section name "BIOC_Base.BioCharacterImporter"
Inside of that section you'll see two important lines. m_femaleActorType and m_maleActorType. To complete the swap take your selected gender (I have heard that using the male can cause issues with facial animations, but I've never tried it) and delete everything on the line after the equal sign. Next paste in your selected party members code. So for example I am replacing my female shepard with Garrus and my line now looks like this.
Thats it! Save the file and fire up the game. Most everything seems to work pretty well after I swapped to Garrus. Good Luck :)
(If you do run into a major problem you should be able to copy the files you saved before you edited back over the files you edited to restore your game. If that doesn't work, well, you might try reinstalling :-P )