Punch hole in leather strap - value? (Cartier)

[Rinz]

Hey all. I'm totally new into the watch world, and yesterday i got my first watch. A Cartier Tank. Bought it vintage, but with an original Cartier leather strap. The problem for me, is that it does not fit that well, either it's a bit too lose or a bit too slippery.

So i'm thinking about going to a watch-place and have them punch another hole in the strap. However; i also bought the watch with a bit of investing thoughts behind; at least that i want to have the feeling, that it will not fall in value. So my question is will a watch's value go down, if you punch an extra hole - and modify the original strap? Or is the value mostly in the dial?

Looking forward to getting a bit more clever.

Best wishes, Rinz