Hi,
you could do something like what is done in load_database service:
https://github.com/introlab/rtabmap_ros/blob/a97efff760720132ced2a607f384dc5d28a0d296/rtabmap_slam/src/CoreWrapper.cpp#L2859-L2991There are plenty of things from the ros wrapper that need to be re-initialized. To avoid changing the code inside rtabmap node, you could create a python node calling "load_database" service to save the previous database and create a new one with a new name, call external rtabmap reprocessing/post-processing tools on the previous database file.
cheers,
Mathieu