Anyway to add a variable to a project file?

Lets say I am working with router config and wan to use gitlab to manage them

The file is setup like this

hostname ‘hostname’
ip address ‘ip address’

where when i generate the file I want to be able to insert different values for the the variables
A
hostname RouterA
ip address 10.10.10.1
B
hostname RouterB
ip address 10.10.10.2