Backlight 5 continues the Pangolin modules (and also supports the old Okapi modules) so any phplugins code you wrote for those will still work. (All my phplugins and custom css customizations from Backlight 2/3/4- all Pangolin- work fine in BL5)
If you move to the new Kookaburra modules, you’ll need to use new code.
It’s good to know ! Thanks Rod