Be careful about "artificially" moving back in for a short time. Recent tax cases have determined that it's "quality" rather than "quantity" that matters. You need to prove that you genuinely moved back in and made it your home (base) again.
I'd say you need a lot more than a couple of bills in your name at the address and if you move back in after putting it up for sale, that suggests you're not living there as your home, even more so if you move back in once contracts have been exchanged.
HMRC aren't daft!
You'd also need to change address on lots of "official" things, like your driving licence, car registration, obviously HMRC and any benefits (child benefit, state pension etc), all your banks, building society, pensions, and share/investment accounts, local council voter registration, etc.
Furthermore, you absolutely CAN'T move back to the same address (elderly relative) after your short period of claiming to have moved back to the house you own - that screams it's just an artificial sham!
Surely the first stage is to work out what, if any, CGT there'd be as it stands. It may not be that much if you genuinely lived there for many years, and certainly may be cheaper than paying for removals vans to move your furniture and belongings back to it, just temporarily, and then to move it all back again once it's sold, plus the time/hassle of changing all the official addresses (twice). Only when you know how much CGT is at stake, and compare it to how much less it would be if you genuinely moved back temporarily, can you decide if it's worth going through the sham of moving back in (and taking the risk it may not work anyway!).