Minor Editing to CAD simple Model

I have made a simple model using Autodesk Inventor.
(please see attached image to help you understand)

All three "arms" are currently 19mm in diameter, but I would like the two arms that don't have the thread on them to be 17.55mm (needs working out exactly) so that they will still slide in the same hole on an identical connector, whilst still been able to use the threaded arm.

For some reason it's not possible to unlock the repeated feature so I can edit each one individually. (or at least I can't work out how to do this)

I've spent hours and hours trying to work this out, and read various forms and to be honest I'm fed up now!

Get in touch, asasp. Shouldn’t take an expert more than an hour...