I have migrated my F35 system from 128GB to 256GB microSD card and extended LVM2. As a final touch I decided to shorten inconveniently long LVM2 volume group name using vgrename (fedora_localhost-live to fedora). Unfortunately after restart system was unable to boot.

Was the only step I've missed editing /etc/fstab with the new VG name or something more?

For the moment I reverted the VG rename using another Fedora machine (renamed back to the old name) and booted once again.

But suppose I would like to rename the VG name. What should I do after vgrename to make sure my system stay bootable? Just edit /etc/fstab and run systemctl daemon-reload or something more?

If the system uses grub as the bootloader then check the various references in the grub.cfg file are correct

There is only one way to see if a system is bootable. Make some changes and see what happens. If you're lucky as you were here, good - if not, restore your backup. Think of it as a learning opportunity.

If you are renaming the vg holding the root lv I'd bet you also need to regenerate the initramfs.