Is it your router or one "on loan" from them?
If yours, note down all of the external settings and do a factory reset.
You can then "play" to your hearts content.
(Of course if anything does go wrong, you can do what I have done before and plead ignorance - mentioning a poercut etc. and get them to send you a new config file

)
(actually, may be better to note down all of the settings just in case the ISP is not as forthcoming as mine - Demon UK - was

)