Adding exhaust tips was popular on the M6G forum … if you look on that forum you will see a long post with pics of slip on options.. I’ll see if I can dig it up and leave a link
@phoebus ---another option; likely more time consumptive and money expensive, than the suggestions above; is to dismount the most rearward portion of your exhaust system (not sure how involved that would be, and your Mustang would be out of service for the duration of this project). Take the dismounted exhaust/tips to a stripping/coating service; have the tips blasted with some media (glass beads, walnut shells, sand?) and then refinished (paint, powder coat, or ceramic) with the black finish of your choice.
Our exhaust tips are subject to a LOT of road grit blasting while we're driving; if it were me, I'd opt for a ceramic coating as it would likely be the most durable over time.
FYI: I had a motorcycle after market exhaust canister/muffler ceramic coated satin black a few years ago. I was surprised the ceramic coating the shop used was air dried, rather than baked on. Took 5 days to air cure; looked great and was very durable--no evidence finish deterioration on the bottom of the can after 18 months of road grit.