You mean RFA8.0 does not support RHEL7.x so you wan to update it to RFA8.1 right?
I think you can just replace RFA C++ 8.x header and libraries with headers and libraries(provided in a folder for Oracle Linux 7.x Libraries) from the RFA C++ 8.1 devkits. Then rebuild the application.
Please note that only RDC named user can download the RFA C++ from Developer Community.