Hey Bruce welcome

Personally, I rarely use IFR ATC, I use Radar Contact (VFR) ATC if I'm using a fixed route on the FMC with waypoints, SIDs and STARs and all, but sometimes I'll use IFR vectors without messing up my original flight plan, so I open (in-flight) the ATC menu, then click open or create flight plan option and make a quick DIRECT IFR route. For this, I know from the beginning of the flight I'll be approaching and landing the airport using ATC vectors so I delete all the waypoints, VORs, etc close to me destination so I have a direct route more or less 100nm from the airport and get the IFR vectors from ATC.
The new IFR route you load in the FS Flight Planner in-flight is only for communications, this means you don't have to reload anything in your FMC, you continue with your original FMC flight plan.