If I change bullet types (length/shape) JHP vs LRN vs SWC for instance, I'd only have to re-set the seating die
Sort of. Not the die body, only the seating stem. Once you have the seating die body set where you want it (crimp or no crimp) then when you change bullets you only need to adjust the bullet seating stem.
the exception is changing cases, from .38 to .357. If you have the seater die set to crimp .38s, you MUST back it off changing to .357s. You will ruin the .357 case (and maybe the bullet too) if you don't. You will also have to adjust your crimp die for the 0.135" difference in case length between .38 and .357.
if you are doing your crimp in a separate die, you still need to check your seater die body with .357 cases, to ensure the crimp shoulder in the seater die is high enough not to touch the longer case. Once done, tis done, and the only adjustment you'll need to make is the seating stem when you change from .357 to 38 and back. (you will need to adjust your expander die, each time you change length of cases, as well)
Crimp depends on die body adjustment and case length. It does not matter what the bullet length is, only that it is seated to the right place.
I'm currently set up for Federal 38 spl cases which are all a tad under spec length, but all consistent so no resizing needed.
Lets be on the same page with terms,
resizing is squeezing the fired case down to hold a new bullet. Its done in the resizing die.
Trimming is cutting excess length off the case mouth. It's done using a special tool, a case trimmer, most of the time.
Chamfering is another step, done after trimming (again with a special tool), and is done to break the sharp edge of the brass left by the trimmer cutting head.
There are "trim dies" but these are rarely used for regular case trimming, they're sometimes used in the process of case forming, which you aren't doing...