Court order is just that, an order to follow, xh does not like that. My year to pick weeks first, xh does not like that.
Likely the reason that your one week vacations are not to be concatenated is so that the child is not apart from the other parent for too long. (My county says we can have 3 weeks of vacation per year but a maximum of 2 weeks per vacation.)
One reason to set aside the time limits is if he's traveling a far distance. For example, one vacation spot I like to go to takes nearly 2 days on the road to get there. If I had one week - or maybe my weekend and a vacation week - then I'd only have a few days at the destination. Another destination, the Rockies or Cascades, are 3-5 days away by road. One week would just be driving to and from and nothing more. I'd have to fly instead. What I'm saying is that there are some vacations where two weeks makes sense. Is this one of them? With the order brand new, is this the time to make exceptions?
To continue that thought... .'making wine out of sour grapes'... .Is there something in the order that is a real problem for you? Maybe rather than "giving in" you could counter with a change you would like. I bet that would shut him up real quick.
As Nope wrote, you could agree
in writing to make an exception to that clause but beware. Ex wants that primarily because he wants to be oppositional and jerk your chain. If you requested the same thing next year he would surely refuse to accommodate you.
What do you want to wager that if he gets you to agree to a change this year then next year when he gets to pick first that he will refuse to agree to you requesting the same, even if the agreement was supposed to cover two years? No reciprocity. Oppositional. Blaming. Guilting.
If there is to be a permanent change, it would probably need to be documented in the court record. Something signed between the two of you outside of court might be recognized by the court but I wouldn't count on it.
I don't want to give in. But I know he will do something to get even if I don't give in. He will use the kids in doing so.
You already know this: He will blame and guilt anyway, if not this then something else. So if you give in it may be an enabling type of sidestepping, it may encourage more attempts.
Clearly he doesn't like following rules and boundaries and so he has to challenge hem to have a sense of Control. The order is new. This is not the time to chip away at it without good reason to do so. After all, you said it yourself, he decided not to work and so he has a lot of flexible time.
Edit: I looked and Independence Day (July 4) is a Saturday. Typically holidays trump vacations just like vacations trump the regular schedule. If it is his holiday this year and not his weekend then maybe he could include it to give a couple extra days for his vacation, if around that time.