Subj. If it could be done using C++ pls tell.
If you can’t delete one single point you could try deleting them all and rebuilding it minus the single point.
I would like to “cut” the spline in realtime, so deleting all and rebuild is not what im looking for(
Deleting and rebuilding is probably faster than you think. Try it out. 
Are you trying to cut it in two, or just cut one point out? Cutting it in two would require a rebuild of both new splines anyway. Cutting just one point isn’t possible in blueprint without a rebuild, though it would certainly be useful to have, even for me.