By default, the LAN address if the vigor is 192.168.1.x. Unfortunately, this is also the network of just about every users home network also. As such, VPN doesnt work (network conflict). Rather than get every user to change their home network address range, we want to change it on the Vigor.

Under LAN->General Setup, are the settings.

I would like to change the address to something more unique, e.g. 10.11.12.x, but dont know if setting it outside of the 192.168.x.y will break anything on the draytek?

Unfortunately, this forum cant handle pasting/uploading images.

Currently, I would like to try setting:

"For NAT Usage, IP address" to 192.168.17.1
start IP address: 192.168.17.20
Gateway IP address 192.168.17.1

The unknown for me is what the gateway IP should be. Will the draytek still use 192.168.1.1? i.e. should I set it to be 192.168.1.1 or 192.168.17.1?

The problem is, if I guess wrong, then the draktek will be bricked, and ill have to reset it to factory, losing all the setup (including VPNs, users etc)

First off, a thing cannot be "more unique" - it is either unique or it isn't.

With that pedantry out of the way, as far as I know you can set the LANS to be anything you like within the allowable private IP address ranges. The gateway address would be the same as the first IP address of the router, assuming that you wish to use the router as your default gateway.

Also,
There is nothing stopping you saving configuration settings at a point just before you change the LAN IP's so that you can quickly get back to that point if you have to reset the router.

John.