substituting a snare drum sample for the original

I’m recording a drum track with the electronic drumset “Roland TD-4KP” V-drums portable set, and I’ve created a snare drum sound/sample (not on the drum kit but on a cubase) that I want to substitute into the track instead of keeping the electronic drum set snare. Problem is, I don’t know how to put this sample in, in order to replace the snare sound on my electric kit in the track.
Things I’m unsure of:
1.) When I try and put the snare drum sample into the track that I have recorded with my electric drum kit, it automatically goes to the start of the bar which is not what I want, when I want on beat 2 or 4 for instance.
2.) I need to keep the hi-hat in the track as well, and it looks like it won’t stay if I insert the snare drum
3.) I don’t want this sound only on the backbeats either, I want it to be a constant feature of the track.
4.) The process to do this.
So is there anyway I could:
1.) Substitute the sample into the track to replace the snare drum sound on the electronic drumset used to record the track?
2.) D