You can indeed. 
Though I think Trust Levels are referenced in a lot of places, so it may be a big job to go through each field and change them manually.
By default, I’d say the Trust Levels are about a certain element of trust in that the extra abilities they confer wouldn’t be granted to just anyone. It takes about 10 minutes or so with a little light reading to get to TL1, which filters out a lot of spammers and bots, etc - and about two weeks to get to TL2, which is a good time to absorb the different culture and rules of the forum you’ve joined. Having them based on how much you’ve read and engaged with the site is generally a good indicator of how well you know it, and how much you can be trusted to use those extra perks to benefit the community you’re now a part of.