Hi @Laura_G,
I just checked and it looks like it is possible to split cells. You have to click into the merged cell, then you can select the Table icon in the RCE, hover over Cell, and pick Split cell.

I didn't see anyone discuss accessibility in the posts above. Merging cells in tables can cause accessibility issues with screen readers; Penn State has a great page on table accessibility and they say:
Don’t Merge Cells
Even with headers properly marked, if cells are merged, a screen reader could find it difficult to determine which cell when cells become merged. Therefore it is recommended not to merge cells.
I hope this helps!
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.