I haven't replaced the CMOS battery in your machine model, and would always advise to remove old battery from pcb for replacement, but from my extensive experience (30 years) withing the computer motherboard and TV / Video repair industry (older PC motherboards had their CMOS battery soldered in) your solution will work OK. It may save you damaging the very fine pcb tracks and thru-hole plating on your circuit board, if you don't have great desoldering/soldering experience.
A few things to make sure of first.....
1) I know this is elementry.....but always check that you are replacing battery with similar type (voltage rating, cuurent rating and chemical construction (ie lithium / ni-cad / etc)
2) Double check polarity before soldering in.
4) Make sure your replacement battery has solder tags on it.....NEVER EVER attempt to solder directly onto surface of CMOS cells....they WILL explode very violently in your face!!!!!!!!
3) Check that you have way/instructions/tools of resetting machine parameters to owners / factory setup.
I know you are questioning whether it's safe to rely on soldered legs to legs of battery, but with a CMOS battery we're not going to have much heat/current within this circuit.....unlike rechargeable batteries within handdrills etc. so there isn't much chance of it parting company and dropping into surrounding circuits and causing short circuits......as long as you overlap the old and new legs before adding solder(ie don't just solder them old leg tip to new leg tip)
What you really have to watch out for is solder splash or blobs of solder dripping onto circuit board......just check carefully surrounding circuitry with magnifying glass before appyling power. If you see any probs, clean them away with pcb cleaner (eg Flux-Off...it comes in a spray can and has an integrated brush on spout)
hope this helps you decide,
good luck with your repair,