First to get new units with different descriptions and cards you need to have changed both the 'type' and 'dictionary' name in export_descr_unit.txt, new dictionary name is used for description in export_units.txt and for unit card name + #.

Re: export_units.txt, thats the right name / place assuming you haven't got multiple BI / RTW /data folders and mixed them up. Sounds like you've corrupted the file somehow, don't know all possibilities but generally you should open .txt files in Notepad or similar really basic text editor, to view you should have word wrap option off, and description lines shouldn't have line breaks in them i.e. you should have to scroll to read the end of long descriptions. My notepad default saves RTW files as Unicode that seems to work.

Re: unit cards, what is displaying if it isn't the peasant?
If you added your symbol outside the original area of the original unit did you also alter the alpha channel to include it? The variations for tga saving in photoshop I thought just related to the x-bit level and the default was usually correct.