changing front brake pads on my 10 plate Jimny.

jackonlyjack wrote:

Definitely do not open the bleed nipple 
 

There are valid reasons to do it both ways - pushing the fluid back through the lines pushes a lot of debris & dead rubber particles back to the master cylinder, releasing the bleed nipple allows that dirty fluid to be ejected, but, there is a risk of allowing air into the system, so that you need to bleed it afterwards.

Given that you more than likely also need to do a fluid change, crack the bleed nipple expel the dirty fluid, fit new pads, use a turkey baster to pull as much old fluid as you can out of the reservoir, refill and bleed, get two jobs done at the same time.

Also, removing the cap.on the reservoir makes no difference to pushing the fluid back.  The cap is vented.

The reason opening the bleed nipple is often recommended is because of debris contamination (as above) but also because pushing back to the reservoir can invert the master cylinder seals on some cars, leading to a very bad car day.  I don't think the Jimny is one of these, but some Vauxhalls are prone to it.