If I have a muzzle pinned device removed from a rifle with a 14.5 barrel and have another device installed and pinned to reach a 16.1 barrel length do I have to do any ATF paperwork for an SBR?
The purpose of a pinned/welded muzzle device on 14.5" barrel is to get past the 16" minimum to not have to register as SBR. If you replace it with a permanent fixture (pinned/welded) to surpass the 16" minimum you don't have to do jack.
No unless you are making it shorter than 16". Removing a barrel to conduct maintenance and/or upgrades is legal as long as it goes back on the rifle a legal length.
The legal length for a standard rifle barrel is of course 16"...the reason for 16.1" is fudge room to make sure it's 16". There have actually been people who messed that up and had to pay up.