Puddletron have a look at the advanced edit button/section column sitting next to the pattern/tracks (you’ll probably have to click the A<->E button to open it up.)
Select if you want to effect the current pattern or the whole song, then click the Expand button (should double the length of the pattern/song.) You can also shrink the pattern as well.
Plus not sure if this is also more advanced (arbitrary length) from Mr dblues box of tricks -> https://forum.renoise.com/t/new-tool-2-8-3-0-flexible-pattern-resizer/30664 