In Microsoft Word, if I have a table, and I want to move one of the internal vertical borders just within a particular row, I can do this by highlighting the row (or just the pair of cells on either side of the relevant border) and moving the border. This moves the border within that row, but keeps the corresponding border unmoved on every other row.
For some reason, the corresponding technique doesn’t seem to work for moving internal horizontal borders within a single column.
Suppose you have two cells, one above the other, and you want to move the border downwards. Do this: select the bottom cell, and use “split cells” to change that one cell to be two rows by one column. Then, select the upper of those two, together with the one above it, and use “merge cells” to combine them.
You will end up with the same number of cells that you started with. But adjusting the height of these two rows will give you headaches.
Its strange that this is straightforward for vertical borders but requires workarounds for horizontal borders.
In any case, thanks for the advice. I ended up just using “merge cells” more staightforwardly as ultimately it turned out I just needed fewer cells in some columns.