That’s a pretty major downgrade – £25 tyres rather than £50 ones so £50 decrease in value overall – what’s that as a percentage of the bike? Apart from the value, as others have said you’ve got a not-very-good at all tyre there instead of a really quite good one so I’d be looking to get it sorted. Those RRs will not be very grippy at all.
You can reject and return for a full refund for any or no reason so it’s in the shop’s interest to set you out. I think there’s an argument for them paying the return carriage too as it’s a fairly major change.
I’d threaten to return the bike and see if they’d rather sell you some of the correct tyres for half price instead? Or ask them for £50 off so you can put that towards the tyres?
Edit – meant to say that the tyres you have will go up tubeless no problem although not as easily as the new Rocket Rons and won’t stay inflated as long. But the significant thing here is that they are a much worse (less grippy, heavier, more puncture-prone) tyre.