is it okay to cut from the nock-end when bare shaft tuning.. the insert is not to be removed when first installed  

Yep

If you use hot melt you can always remove the insert and cut from the point end. This is how I do it and so does everyone I know.

You can use saran wrap or plastic food wrap to tune also.I tune all my carbons this way,I'll push in the insert with alittle saran wrap to hold the insert in snug.It holds them in tight enough for shooting and tuning,but you need a softer target like a bag target that doesn't grab too tight to pull the insert out.I use this method for MFX and regular carbons,I don't like to cut from the nock end because I like to tune with my arrow wraps on the arrow.