No. You can specify only a single singer for one part.

If you want to switch singers, you can create multiple parts and assign a different singer to each part.

In Cubase, you can create multiple parts in a single track. This allows you to assign multiple singers to a single track.
However, the waiting time configured in the "Preferences" window is essential to synthesize consonants.
If you want to assign different singers, you must insert the waiting time between the end time for the first singer and the start time for the second singer.
If notes exist within the range of the waiting time, the notes are not voiced due to delayed synthesis.
If two parts to which different singers are assigned are adjacent to each other, it is best to create those parts in separate tracks.

When a single singer is assigned to different parts, any neighboring notes can be voiced normally.