Here's what I'd do if I din't know for sure what was going on.
Since you are now apparently needing a possible professional setup - I'd try it myself first to see if I could get as close as I need.
If I messed up - then off to a luthier.
BTW: MOST GCs have an on-duty luthier for just this purpose.
Here's the one in the local (to me) shop in Murrietta, California :::
This guy's good and the prices are all set - so there's no Aha! moments when you bring it in. They've prolly seen it all before too.
GC is making a very good move by taking their individual luthiers out from somewhere behind the store to the inside-the-store placement to answer questions and generally curry favor and communication with customers.
It works for me and I have a greater sense of customer loyalty to a store that recognizes me and greets me by my name.
I cannot guarantee this is at all GCs. The one I go to is a lower-mid sized store and they have this going for it, so it may become a lot more available in all their stores later, if not sooner.