If you’re talking about how Cubase handles the musical notation when you change from 4/4 to 7/8, Cubase will notate the time signature change correctly and adjust the bar-lines accordingly.
So, if you’ve recorded a four bar phrase, say, of 4/4 with 8 quavers in each bar and played it with the standard 4/4 beat stress of strong, weak, medium, weak then it will look (and sound) like this in Cubase (imagine the upper case letters are crotchets and the lower case letters tied quavers):-
4/4**|S W M W|S W M W|S W M W|S W M W||**
If you then shift this to 7/8 time, Cubase will notate the same phrase like this:-
7/8**|S W M w|w S W M|W S W m|m W S W|M W – -||**
However, note that the beat stress pattern hasn’t changed - Cubase won’t do that - so the recording will still sound like a phrase with a 4/4 rhythm when played back in isolation because the ear will follow the beat stresses.
If you want to hear a 7/8 rhythm then you need to not just set the time signature to 7/8 but also play your phrase with an appropriate beat stress (perhaps 4/8 + 3/8 or 3/8 + 4/8) when you record it.
Written time signatures and bar lines are only notational devices; the rhythm is determined by the beat stress you hear.