Tough one.
I would think if the customer negotiated for new signs, they won't want a patch on it without reducing the cost a great deal. Afterall, he's saving you much time and material on your end and accepting an inferior product.... all the while you might get a bad rap if you don't give him exactly what he bargained for.
I'd do them over.
Here's a similar one. Well, not quite, but along the same lines.
Had two big companies locally do a merger. We got the contract to re-do their signs. They opted to go with 3" x 22" white on black vinyl patches. Black backgrounds and white lettering for those not following.
We printed out almost 2,000 of these, plus numerous banners and other signs. A few days after they were putting the patches on, we get a call. Hey, we asked for black and these things are kinda grey. Yeah, right. Black is black and although your own signs vary from old ones to new ones vs substrate to substrate..... we can't match all the different blacks you have or it will become a whole lota custom runs. What's the beef ??
Ya see, some of our agents think they look a little different and people can see that there was a change made.
Ummm, well, wasn't there a change made ?? Didn't you all change your name ?? Didn't you get new phone numbers ?? Aren't you getting all new stationery, invoice, contract, business cards, signs, magnetics, and so on ?? Doesn't that constitute change on your part ??
Uh-huh....... but the agents think the signs now look like they've been patched.
I didn't exactly lose it here, but I laughed and said, what the heck do you think you ordered ?? You asked for patches, because it was far less expensive to buy my PATCHES [as I've called them all along] and put them on your existing signs, than for you to go out and buy 900 new ones.
Well, these are real estate agents and you know how they can be.
Too bad, you ordered white on black printed vinyl, I gave you several samples to be sure they were alright and no one at any point rejected them from the owner's to office managers, so don't tell me I'm gonna take orders form a bunch of agents.
If they are going to be this anal, we'll make them after this bill is paid and we'll custom make the replacements for those who want or need them. Let me know how you want to proceed.