I feel like I must be missing something quite simple here!
I have a closed polysurf (a hollow steel bar).
I have used ‘Boolean Difference’ to make a hole (with a specific shape and size) in the top of the steel bar at one end.
I have since realised I need to lengthen the bar, however if use Scale1d it will warp the hole.
I have tried adding another chunk of bar onto the end with the idea of seemlessly joining / blending / merging (?) it but have also got stumped here too! I have tried all the commands I know, and have scoured the internet for more but am still at a loss!
You can use ctrl+shift to select control points and move only the ones at the end. Or if the end of the beam is planar, sub selection works on faces too.
Or you can turn on the points explicitly then select them normally and move.
The other method can work too (fetching an additional bar to the end and merging those), assuming both objects are solid, you can use BooleanUnion first, then MergeAllCoplanarFaces to get rid of additional seams. You will probably end up with additional points too, that you can delete at the end or use RebuildEdges for simplification.