Taking them apart doesn’t invalidate the warranty.. Tell your LBS mechanic to MTFU!
This isn’t what Fishers told me. Lower leg service fine but anything more should be carried out by a SRAM technician as to not invalidate warranty.
Either way its a piece of cake.
Have a read of Peter’s (of this Parish) guide to changing the spacers.
Travel adjust link
I have fettled with mine loads and they have always been fine coming apart and going back together.
Just take your time and make sure you have everything before you start.
I think your LBS is a bit too risk adverse or it just wasn’t worth their time either way perhaps time to change LBS 😀