You'll have to open up the barrel channel to accept the larger barrel and likely the recoil lug, then bed the action.
Yes you can have a brake installed and you'll LOVE IT. The brake I highly recommend and is being put on my custom build is the LR Customs T-Rex brake. Its a tactical brake and not a radial. It tames these rifles!!! I've had a radial on my BP Xpress and its no match for the T-Rex. I have a friend with a T-Rex on his RUM and he can see the bullet impact his target.
Best thing you can do with that rifle, is to send it to LR Customs and have Levi install the ASG Gen2 breech plug and install his T-Rex brake. Replacing the OEM breech plug is the first thing anyone with either a RUM or UF rifle should do IMO.
There's no weight on the sled and the charge my friend is shooting.... WITH the ASG Gen2 breech plug from his RUM, is 100grs by weight of BH. WARNING..... THAT CHARGE IS NOT FOR PRODUCTION MUZZLELOADERS! READ AND FOLLOW YOUR OWNER'S MANUAL.
This is how well a T-Rex brake works with a heavy charge....