If you can't accept it and you have no way to exchange for a different last that works better for your foot, then worst case scenario just use them as beaters for rainy days.
But really, just wear them and enjoy them, it's just a crease.
Honestly, at $1,800 a pair and with a reputation to maintain, St. Crispin's should offer to remake your shoes. They have made more than enough pairs to know that this type of thing can happen, and should have warned you that this pair could have these types of stretch marks. You aren't some litigious asshole and you know what nice stuff is. It would not be rude or gauche to ask them to correct this problem.
$1,800 for a pair of shoes is probably be equivalent to driving a Porsche 911 Turbo S in the car world. Imagine if the headlights started fogging up. You'd definitely bring it in to be corrected and Porsche would do so free of charge.
It would be a disgrace, however, to treat $1,800 shoes like beaters.
I don't know, brah, but $1,800 for a pair of shoes represents a step below the highest echelon of the market (i.e. Lobb bespoke). Perhaps DWF can chime in, but I'd be interested to know how hard it would be to pull up the leather and put in a new toe puff. If my $300 Allen Edmonds do the crinkly toe cap thing, I can't really complain, but if my $1,800 custom St. C's went limp on me, I'd be a little miffed. Your shoes, your decision.
It all depends: if they measured your feet and then came up with this result...then they really should fix it.
However if you just ordered the size you deemed fit, then it's up to them to decide and they might well agree to fix the problem in the interests of retaining you as a loyal customer.
No harm trying....FWIW i have a number of calf shoes and the majority of them do not show major creases....in fact my SC chukkas have behaved well in this respect.