Is it a problem to open the flaps of diapers on Shabbos because they are stuck together?
The concerns of opening a diaper for the first time on Shabbos touch on either the Melachas of מכה בפטיש or קורע or תופר, therefore by opening the diaper before Shabbos, (it does not make a difference how much time in advance) and then re-closing them – this circumvents the problems.
There is no difference between Shabbos and Yom Tov in this matter.
It is also worthy to mention that the diapers which are made with velcro, do not have questions in the first place, thus they are certainly permitted for usage.
See Shulchan Aruch Admor Hazaken Orach Chayim 317:6 & 340:13. See also Minchas Yitzchak 5:39 (who rules that it is forbidden to open the plastic of a band-aid).
The solution of opening the diaper once and then closing is offered by Shemiras Shabbos Kehilchasa 15:87.