"First, if you remember I was toying with the idea of making a crossbow skill, however, I have no clue how to create new skills, what file is this information located in?"

Skills are implemented in and by the main .exe file. To add and implement new skills,you'd have to be able/willing to modify the game .exe, and I won't help you with that, 'cause I don't 'do' .exe changes.

/*====================== Question 2 =======================*/
/*=========================================================*/

"Second, I'd also like to create pre-existing characters like you find in MM8 but again I don't know how or even if you can do this in 6 and 7."

The creation of pre-exisiting characters is simple enough (in MM6/MM7), but to add/dismiss those characters to/from your party at-will (other than in the capacity of a hired-hand) requires that you modify the event language and the event language 'interpreter' in the main .exe file. Once again, I don't 'do' .exe-file mods.

/*====================== Question 3 =======================*/
/*=========================================================*/

"Finally, I noticed you figured out how to add new quests, I'm not looking to add new one's but just switch some, for example let's say in part 6 I want to have Wilbur Humphrey give the Priest promotion quest instead of the Paladin quest, I've tried editing the quest.txt, the npcdata.txt and the 2Devents.txt and have had no success, any suggestions?"

Quests, like all other unique game events, are controlled and implemented by custom event-code sequences. These event sequences are 'global'in-nature and can be (normally) found in the GLOBAL.EVT structure within the events.lod file. To 'safely' re-assign a quest, you have to export the GLOBAL.EVT, locate the quest event, and modify the code and/or code parameters and/or QuestBits. Although this is a simple task, getting 'ready' for this task requires that you locate/break-out each event sequence from GLOBAL.EVT and "parse out" the syntax for each sequence. Obviously, you'll have to learn the event language as you are parsing out the syntax by emperical methods (observation/analysis, trial-and-error and the-like). If you are serious about making this and similar game changes, let me know. I can help you get 'started'.

BDJ ...