Anyone ever successfully used a cockpit PE set meant for same plane BUT of another brand?

Often.

Not a lot of detail to the story...but since I like to build old Airfix, Frog and Revell kits for whose a/c types the P-E is designed for Tamiya, Hasegawa etc...you just make do. Sometimes you have to trim or adjust, most often thinning cockpit walls and such, but adding 'someone else's P-E' is often easier than scratchbuilding.

You just have to make a plan...go slow...and test-fit everything half-a-dozen times, to check the fit. Not much different than you have to do for the 'proper' kit...where things don't always fit smoothly or properly, either. 

Ditto what Greg said.

Jim 

Stay Safe.

I haven't done that yet with a PE set because I haven't had to, but I did do it fairly recently with a Quinta Studio 3D-printed cockpit decal set that was meant for a Trumpeter 1/32 Su-25.  It was the Trumpeter Su-25 I was building, but I was using an aftermarket Aires resin cockpit set.  Had to make a lot of adjustments here and there...building up side walls.  adding scratch-built details to change it from an Su-25K to an Su-25M1.  It was a big job, but like Greg says, it was still a lot easier than scratch-building everything.  The 3-D printed decals though were MUCH easier to modify than PE, since you can easily cut and trim them with a knife or scissors.

It was a lot of work, but it doesn't look like every other Su-25 model cockpit out there, so it was worth the effort.  Now if I can just get my motivation back to fix the alignment issues on the bottom of the fuselage...

Giday mate
In truth, most detail sets or PE can be used on pretty much any model of the same type. Sometimes you'll have to "adjust for fit", but I've never found a set that is impossible to use in some way or another.