Regardless of the option you choose -- the cutting hack or the direct replacement, you'll need to do some soldering if the RTC is not socketed.

If you were to cut the sides of the RTC in-place, you would have to be extremely careful not to hit the motherboard. Most people use a Dremel to cut down to the traces you need to get to, but it can catch and fling the Dremel away from the intended cutting area and you'll hit the motherboard.

The safer option is to desolder the RTC from the board and either replace the RTC using a DIP socket with a new one (preferred), or you can remove the existing RTC to modify it and then reinstall (resolder) it in place.

Here's a pre-made RTC drop-in replacement with a CR2032 button cell battery.
or
Mouser carries newly manufactured DS12877+'s compatible with the DS1287: https://www.mouser.com/ProductDetail/Ma ... mlI%252B13
and
DIP socket: https://www.mouser.com/ProductDetail/?qs=dNsY … dZQyTNNzA%3D%3D

Hopefully someone local can help you out if you're not comfortable with soldering. You can also look in my signature at the link for soldering help. I uploaded the whole IPC rework manual which has step by step pictures. On YouTube, you can also look at EEVblog for great soldering tutorials in video format: https://www.youtube.com/watch?v=fYz5nIHH0iY

Cheers wiretap! [edit - oops soz]
That's marvellous information for me to get started with, thank you. I can't see where there might be either a line to indicate a socket arrangement - or little holes for a pincer tool to get in - and I used as much force as I dared to try to wriggle it free - no go.
I've been brought up in a family without interest in flux stations, soldering experience or electrical hobbies etc - I feel like I've missed out 😀
Again - really appreciate your time to advise on the matter -will have to get back to this later, late here in Oz

PS finally worked out how to attach...

Thanks again, wiretap for your info and cautionary advice -
I have learned the hard way that the dremel bit can have untoward consequences. Attached are snaps of a "new" Dallas RTC that I performed the hack with - but inadvertently hacked off Pin 15. My attempts to resolder a new pin (with wire from paper clip) got messier and messier, as the 2nd shot shows after I was getting too cosy with the resin 🙁
Dread to think what I would (?) do over an unprotected motherboard...

Cheers

Good job ! Is that some of that Double sticky foam under the battery holder ? Good idea !

Well spotted, Horun - 'twas indeed double-sided tape! Thanks for your kind comments - literally the first play with My First Dremel. *Next time* I do something like this I would embed the pins in a protective sponge etc - the plastic packaging was too restrictive, so I went "Commando". No such commando heroics if I were to attempt the on-board modifications wiretrap warmed about - even if I were to cover the circuit-board with high-density foam matting etc during the surgery, getting the angle of the dangle for successful connection to Pins 16 and 21 would be nigh on miraculous for me. I couldn't manage the pin replacement though I have "seen it" completed on various web sites.
Work In Progress...