You can edit existing sound files. You can replace if wanted. You can also add more sound files. The sound files are in Z:\OOTP Baseball 20\data\sounds for OOTP 20. OOTP uses OGG files. Previous versions used WAV. I think both can still be used.
1) adding files: if you want to add a new file save it as the next number in succession. For example a new ambient file would be ambient10.ogg and a new rally as rally26.ogg.
2) players can have their name announced. You can also make walkup music. For example you would create bart simpson.ogg and this could be played during the game but not necessarily at the beginning of his at bat.
3) to edit or create sound files see this post by Bobble.
https://forums.ootpdevelopments.com/...ghlight=bobble
4) Audacity can be used to edit and export to OGG format. It's free.
https://www.audacityteam.org/