change to an x percussion -type notehead temporarily

Use the Inspector or the noteheads palette

If you also wish for some kind of playback for the x noteheads - e.g. handclaps, tambourine hits, etc, - here's a (somewhat protracted) discussion:
https://musescore.org/en/node/271906

An example with playback, using one of the methods discussed in the link above.
Hand_Clap.mscz

Regards.