Trimming the front is normally inadvisable given the nature of how the front is knotted compared to the rest of a hairpiece.
The knots in front are normally single strand and bleached, as well as staggered or gradual in density.
Cutting into it removes the "artwork" or whatever you call it, and leaves you with whats behind it.
However, with carefull consideration and patience, I have been able to reshape a front satisfactorily, but not quite as good looking as it would have been if it`d been made to that shape to begin with.
What you need to do is trim it by cutting only the base and without cutting any hairs. I use a small set of sharp scissors and I open them only wide enough to fit the lace in. That way I dont trim (many) hairs.
The hairs that I do trim, are left with very short ends sticking out plus the knot is left in there too, so I wet it down and slowly, very carefully pull thses short ends plus their knots out.
I`ll also remove a few other hairs here and there to recreate the staggered/gradual hairline that I messed up by trimming the front.
Plan to spned an hour and a half to do a good job. also keep in mind that a trimmed front will fray and wear out faster than an undisturbed front.
As far as color goes theres only one color chart, or color ring but sometimes its a matter of opinion when matching the colors since alot of them look so alike. One guy will look at a hair sample, hold it to the chart and declare it a color #20 while the next guy, squinting, will say naw man, its a 20R.
From what I know, those two colors are pretty close.
With densities, I dont know anymore than you do other than, 65% coolpiece density is quite thin.
Who`s selling 90% density stock pieces?