I replaced it and rather simply. From the top, no need on my 2005 GT to take off the wheel and arch liner, in fact I think it would have still been awkward to get at. There are three fastenings on the coolant bottle. As shown on my first picture. I removed the engine cover though am not sure you need to. Gives a little more room.
Remove them and take off the overflow pipe and stuff a screwdriver in the pipe and re-tighten the clip to avoid coolant loss - picture 2. Once the three bolts are removed you can move the coolant bottle with main connection still attached to one side on top of the engine
Looking at my third picture the red circled pump is for the windscreen, the green is the headlight washers which don't work on mine anyway.
Lastly the feed pipe to the washers when removed is likely to break off the nozzle on the old pump so if you are just checking then be careful. The plastic seems to be very brittle, probably with age.
My pump just pulled out of the bottle. The new pump came with a new seal but I used the existing. I attached the feed pipe before push fitting the new pump.
I needed Molegrips to remove the old pump. I had a new one so was not bothered if it broke which along with the nozzle I mentioned above it did.
I also found when the new pump was attached I still had no spray. Both nozzles on the bonnet were removed and left to soak in soapy hot water. I guess they were blocked and the old pump a bit tired, burnt out.
The bonnet insulation clips break on removal, I find with trim clips this is the norm now. I need a few new ones (had some spare).
Having the coolant bottle removed helps considerably when changing the headlight and fog bulbs as I did afterwards.