Create a separate file system to /var/tmp sub-directory.

Greetings ,

I need to create a new file system to then mount /var/tmp subdirectory. Do any of you know if there's a need to reboot the OS for the changes to take effect. The idea is to:

1.) Create a new Logical Volume.
2.) Create the file system.
3.) Mount it to a temporary directory, i.e.: /mnt
4.) Sync /var/tmp data to /mnt
5.) Umount /mnt
6.) Delete /var/tmp content to release that space.
7.) Mount new file system in /var/tmp

I'd like to know whether this can be done "online". My concern is whether I'll be able to delete all /var/tmp content because some files could be being used.

Is there any procedure you could share to do this modification?

Thank you!