To “permanently” enable rndis_host please see how-to-load-rndis-host-module-on-usb-plug-in
For occasionally using it you may just issue (as superuser) modprobe rndis_hostand answer “n” when the system asks if you want to permanently un-blacklist it, so that the module will not be loaded on next reboot.
Re. how “safe” it is I think that just occasionally connecting to your phone from a laptop that is regularly backed up (or where there are no vital data) is reasonably safe, but I am no security expert so don’t take my word as a recommendation.