As your picture shows your ext shower above the skirt and what appears to be a storage cab next to it, might also check in there for an access panel. I would find odd if there wasn't an access, somewhere, especially if hard plumbed with pex tube. I could not remove our faucet box if I wanted to without first removing the water lines to it.
If your unable to find access-a call to Lance might be in order.
Curious on the cabinet above skirt-isnt your bath behind there in that corner?.
I don't see any wrong with splicing hose if needed. As you'll have extra hose if barb fitting I assume to splice, was placed far enough down so it wasn't trying to slide out the hole in box -catching which could be problematic.
Another option, as a last is check your hose(s). What you would do if could find just an end, or cant get to other to remove hose. I removed ours to cut off end of hose that folded creased. Ours the ends that are swagged on, center piece has hex lip. It can be unscrewed, very slowly. Allow threads to turn, as its fairly soft material would be easy to twist off.
I used a large cresent so I could keep constant pressure on hex. Again unthread slowly, Hardest part because hex is so thin if wrench not perfectly parallel it slips off. Then a few figure 8's on a piece of wet/dry paper to reface hex.
Lastly, the male threads are standard 1/2" IPS. So a barbed swivel fitting, or a Flair-It could be used, or entire water supply flex line to replace.
But I cant imagine there is not access ..
Good luck.