You don't need a conditional for that, it's already built into vBa CMPS.
Assuming that you already have more than one style installed, just go
ACP =>
vBa CMPS =>
Edit Pages =>
{select the CMPS page you want to force the style for} =>
Go and then change the
Custom Style for this Page value to what you want.
If it doesn't work as expected, check out this thread
here then and do the edit in post #6.