Dropping the trigger group out of a BPS ...is not a big deal / and with a little bit of common sense and attention to detail, its easily done ...and does not damage anything.
Yes, I understand Browning says ... "No further disassembly for normal maintenance is suggested" - beyond removing the barrel, etc.....but manuals for a lot of shotguns don't suggest you take a gun apart past the basics.../ but that's probably because they think the average shooter is incompetent when it comes to basic mechanical skills - and will take a hammer to it or something stupid and expect Browning to fix it after they break it. Its a sad commentary on our times, in my view
In fact many of us will take any brand new pump gun apart - before we shoot it - just to get the extra grease and preservative out of it from storage and shipping....and lube it and reassemble before we would ever shoot it ( and all of the guys I shoot with feel that way - but we're all over 60 yrs old too - and know how to do it right ! ).
Some of us even take the stocks off of our Browning Over Unders at least twice a year - to clean them out as well ...and you will see that is not suggested by the mfg either...but I think its smart to know how to do it right / and to maintain your gun properly - or you could pay a gunsmith to do it - if you're afraid of doing it.
Like FITASC said...taking the trigger group entirely apart is a different deal - and should not be done unless you have the experience and knowledge to do it...
but dropping the trigger group out of any brand of pump shotgun - might teach you something about your firearm..../ and done with the right tools and some common sense....can be rewarding / because you're taking better care of the gun in my view. As a long time shooter - and hunter - I take a lot of pride in knowing how to take a gun down - and in teaching that skill to my grown adult kids - and now my grandkids ( on shotguns, handguns, etc...)....but heed the lawyers that wrote the owners manual if you choose to...