On the TF, it is quite easy to change the front of rear-subframe mounts without dropping the subframe.
Leave one front mount on and work on the other one - this keeps the subframe in position. I took the weight of the car on the side I was working on at the back of the subframe - and also at the sill jacking point wuth an axle stand there. The reason for this, is that you want the subframe to drop a fraction when you take out the two bolts holding the flanges in, to increase access to the bolthead inside the mount. It doesn't drop much, but even a half inch helps. So, my advice is not to support the subframe at the front on that side, so it twists slightly lower when those two flange bolts come out (these are prone to snapping btw - get yourself a set of cobalt HSSG drills).
The problems are that there is little space to get a socket into the front mount to hold the bolthead, and the bolt is too long to come out even if you do get the nut off, as the bolt trikes the chassis in front.
These are not fatal problems. A 1/2" drive socket will get into the mount if you have taken the flange bolts out and supported it like I said. It's a bit of a jostle to get it in, but it will go in.
The next problem is that the bolt is loctited and the torque to get it off is huge. I jest not. Heat it up. Do not try and remove it cold. If you get it hot enough to boil spit it'll undo wth ease.
The final problem is that the long bolt running through the centre won't come out as the head strikes the chassis. Simply angle grind the end off a few threads out from the nut before you start. This is enough to allow it to come out and you can reuse it too in reassembly if you like.
On reassembly, you can either reuse the shortened bolt, or cut the new one down to the same length, or use a full length one but put it in backwards* - so the nut is inside the mount, instead of the head. This allows the bolt to be withdrawn backwards where there is plenty of clearance, as opposed to forwards like before, where there is none.
(*didn't try this, but I don't see why it wouldn't work).
I have used this technique on both my rear subframe front mounts and there is no difference between the sides. Do one side at a time so there is always one front mount in position. If your front mounts are very corroded you might want to support the subframe on the side you are not working on as well as the remaining front mount will suffer additional loading when you remove the other.
General arrangement of axle stands on the n/s. It's up to you to make sure your arrangement is safe and suitable.
Left - old front mount and long bolt with the end angle ground off to allow it to be removed. Right, shiny shiny new front mount and yet-to-be shortened new bolt. Could have resued the old bolt frankly, it was in very good condition, having been screwlocked.
The obligatory snapped flange bolt (right). Get yourself a decent HSSG drill to deal with this. It is hard to get this particular bolt drilled out though - the sill interefers. I drilled a pilot hole with a mini-dremel with flexible extension shaft, which has a small enough diameter to not foul the sill. Then I used bigger drill to open out the pilot hole. This fouled the sill and went in at an angle, but the piloy hole seemed to keep it on track. Choose your final drill size carefully to avoid losing threads - it is something like a 7 or 7.5mm, but check.
Note that although there appears to be an axle stand supporting the front of the subframe in the picture below, it was just belt and braces - there is clearance between the top of the axle stand and the subframe. I didn't know at first how far the rear subframe would drop when unsupported on one side so wasn't taking any chances. Not far at all, as it turned out.
Now here is a confusing photo - at the time I took YYG10005A bolts out of the two flange holes. Consulting the exploded diagram in Rimmer Bros I saw that in fact they should be the self-tapping (helical groove up through the threads) KYP100002(L) bolts. I bought these and they were useless. They wouldn't tighten - they stripped their thread near the head of the bolt. So, I went back to using ordinary bolts at this point, but it looks like the YYG's are in fact correct, although not as shown on the general assemly drawings. I have no idea what is going on there.
See, I told you you can get a 1/2" drive ratchet in there - note you can see the socket because the front mount has a huge rust hole in it.
Injecting Dinitrol ML cavity wax - pretty much everywhere, but in this case in the cavity behind the front mount flange mounting threads.
The finished n/s front mount - using new but cut-down bolt.
View of the painted rear subframe - I did this before refitting the front mounts, so I could paint around the front mount area. Note in the top left of the picture, the rotted engine air induction hose just visible. I removed it and repaired it with a double wrap of duct tape, as duct tape seems to survive everything...