I do believe there is no rolling back of your project, also Epic does not offer older hotpatches for download.
Certain FBX import created crashes a few version back but they fixed it, I believe it was 4.9 that crashed for me when importing.
What I did then was to set up an older version that still did the FBX import correctly (for me it was 4.8), create an empty project that I used only for importing FBX and then import and save FBX files there and afterwards migrate the resulting assets to my main project which used the newer engine version