10" wheels not a huge problem - I purposefully specified them on my trailer (a Snipe R750)- otherwise I was going to loose a lot of Nav lights & aeriel mouhts off the top of the A- frame on the garage door.
From memory it will depend on what wheels you have. There is some commonality between hubs & PCDs (my old trailer was unbraked and I could have put a set of 8" wheels on!) As you are upsizing there is likely not going to be an issue with the load bearing capacity of the tyres.
There seems to be a bit of bad luck on here with getting reactions from Mersea (Who now own the Snipe brand), although I've never had a problem with them. Hub & stud PCDs are fairly standard, just make sure your 13" hubs are EXACTLY the same as the 10s. "nearest metric equivalent" is a big expensive accident waiting to happen.....