First of all: It is Your Mini, do what ever You want and decide for Yourself if the technical and financial difficulties mentioned from the others are worth it!
But in my opinion You should also consider to You decision the look and if want to deal with the criticism of "Mini-Experts".
In my eyes 10 inch wheels under 12/13 inch arches (and vice versa 12/13 inch wheels under 10 inch arches) somehow don't look right. Technically the 10 inch wheels are only 4-6 % smaller and and the speedo would read a bit more but not enough to care really at the exact Mini speedos
So my advice is to a) try to borrow that wheel or maybe a 4 spoke revo to put under Your arches to check if the look is what You imagined and or b) search the internet for a similar setup, like Your preferred wheels under sport pack arches.
Even the sport pack are still a bit wider - I think - the aesthetics work similar, so what looks good on sport packs, in my eyes also looks good on the cabriolet.
On my Cabriolet I removed the body kit, installed chrome bumpers, special arches and 10 inch revos. Especially in Germany at every Mini meet I got comments about "How could You have ruined such a special and rare Mini." Sadly more often than not, that are also the first comments I typically got. It's tiring...
On L2B last Year sadly I also got my first such comments in the UK.
To be clear, I don't moan about the people, who I had a nice conversation with and told me, that what I have done to my Mini don't fit their taste. That's perfectly fine, because if we all would have the same taste, we all would drive red Golfs...
I talk about the guys that only came over to tell me, I am an idiot that ruined my car...