I have just fitted a C14 rear shock to my C10. The preoad adjusting hose comes out on the left of the bike, and I'd like it on the right.

Does anyone know if compressing the spring would allow the top and bottom mounts to be rotated 180 degrees relative to each other?

Just take the shock out and fit it the other way around.
You need to rotate the top part so easiest to just remove and refit.
The top may rotate with the bottom still attached but that may also cause damage and the extra time to remove and refit it correctly is not that great.

Just take the shock out and fit it the other way around.

Should have said the bottom fork is not symmetrical. It's contoured in a way which interferes with the linkage if turned round.

From what I know of shock construction it should be fine but I have never done it.
I just looked at some pics of the GTR1400 shock and I see there is a shoulder between the 2 sides of the lower mount that is going to interfere.
Hopefully you can spin it around.

Otherwise, resell that shock on eBay and buy a ZZR1200 shock instead.
They don't have that shoulder between the mounts and only raise the rear by about ½".

I've answered my own question - yes it works.

Result! 😁