Is there an analogous way to perform something like the Slice Assembly for neighboring Sentinel-1 paths?
Yes it’s called mosaicking, use the one under the radar-menus.
That lacks the advantage of preserving meta-data though? I am guessing the best way to go about this is to just create two fully processed products and then mosaic? I was just hoping there was a way to go about this more efficiently, as in the case of S-1 Slice Assembly.