Anyone ever done this? Mine looked really old so I today replaced the entire shell.

Problem is, my broadband speed is now about 1mb slower?! Could that just be down to several reboots of the home hub?

Also, is it illegal to replace the entire box with a new one?

Thanks

Yes I replaced mine a few years ago which passed a look at by Openreach when I needed to get them out by '' Oh I see you have the new type''.
Yes it is illegal because some plonker might connect it into the electricity supply and shock an engineer down the line but if all looks well you would hardly likely get prosecuted.

Rebooting a lot in a short space of time may well put you on a lower profile/speed.