I got Fipps spayed 10 months ago when she was good two years old, after two seasons. I worried about coat changes, but so far she looks absolutely fine. There is a little undercoat pushing through at the legs, but I can deal with that easily. When you go to shows you see lots of different Welshies there, some are so hairy and wooly, wavy coat and so on, really makes me wonder how they made it to Crufts for example. But I'm a bit naive there and totally inexperienced. And I agree with Selina, clipping is the worst you can do. But if Fipps' coat should explode I probably would clip her. But once you start clipping you have to carry on on a reg bases.
This is a neutered few year old male Welshie (and he gets clipped too because he looks like that after a while, or maybe he looks like that because he got clipped

. Though his owner said that six months after neutering his coat exploded and she started clipping him)

But Fippy looks like that (photo is three weeks old)...so far so good

Have you seen
this thread ? This thread is a half year ago and Fipps hasn't got any fluffier since at her legs and her coat at the back hasn't changed either since.