bindfs lets you mount directories as other directories
optionally, modifiying their permissions.

Linux only, for BSD see nullfs.

Documentation

man bindfs https://bindfs.org/docs/bindfs.1.html

Usage

# cli
bindfs -u www -g nginx /mnt/mywebsite /usr/local/www/mywebsite

# /etc/fstab

/mnt/mywebsite /usr/local/www/mywebsite fuse.bindfs