Re: Crawl space entrance is too small - can I enlarge it?
Not sure why you're getting surprised responses from tradesmen, as this shouldn't be too big a deal. A 24" wide opening is pretty spacious, so this should just be a matter of adding height to the opening. You can cut the bottom of the opening down to the sill plate (board on top of the foundation. If the sill plate is anchored on either side of the opening, then you can remove the sill plate too if you want. To raise the opening, you do not want to cut anything structural, unless you've reinforced the structure to withstand alteration. Having said that, you can cut siding up to the bottom of the structural support.
Before you start cutting anything, however, I recommend that you do some careful inspection and measuring, then see what kind of access covers are available so that you can cut the opening accordingly. If you are going to make a custom cover, then you can do whatever you want.
This can't be stressed enough, DO NOT cut any structural components without reinforcing the area properly beforehand.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!