I'm hoping for some help, I'm stumped with this.  To describe how I made this initially: I had an enclosure, with draft, no cutouts in the sidewall.  In the assembly, I made a reference plane to indicate the lowest face of the PCB (with the narrowest dimensions due to draft).  This ref plane was below the parts and mate in the assembly feature tree if that matters.  I did an Insert Component > New Part for the PCB, then the part sketch was on the ref plane and made by the Intersection Curve with the inner faces of the enclosure side wall.  This gave me the outline of the void within the enclosure at the level of the PCB.  I then used this outline, did an Offset Entities 3mm to leave a gap, and ticked the Construction Geometry: Base Geometry box to give me the desired outline of the PCB board.  Extruded to desired thickness, everything was good.

After adding some cutouts through the sidewall of the enclosure and some ribs for a captured nut, my PCB part (attached) started throwing rebuild errors (I'm assuming cause the original construction geometry was altered).  Trying to repair the sketch, there were some little line segments within the construction line outline and some gaps.  So I fixed those.  But I'm still getting errors, and if I try to edit the offset value in the sketch it tells me "Reversing this offset would result in invalid geometry.  The previous sketch state has been restored."  I get this error for any attempted change whether reversing direction or not.

Any help to solve the immediate problem?

Is there a way in the future that if I use some reference geometry to build a part, that I can then break the link such that changes to the reference geometry won't enact further changes on the other part?

Thanks!

[Edit: I've repaired it myself through a brute force method, which wasn't elegant or pretty, but works.  However, if someone can answer the bolded question, I'd really appreciate it]