What this parameter does is change how routes are created on the client once you connect to the VPN.
With the default setting (delete_create), your conflicting local routes are deleted and recreated with lower priority along with the VPN specific routes.
With the "modify" setting, the existing conflicting routes are modified to a lower priority and the new VPN specific routes are added.
I can't say to what extent this has been tested.
However, on the surface, it appears it should not cause an impact on other user/usage types.