Sorry for the delay in replying, I have had to complete some urgent work and thanks for all your suggestions.
Anyway as promised here is the NOT very spectacular tool I made up.
Even so, it does work very well but as Puffs says, it's not a job you need to do every day, so maybe this tool would useful for an MZ mechanic
I did consider using a made up puller but the spring is extremely powerful and after testing the stretch, was convinced that if pulling it upwards it would actually lift the bike off the ground but I suppose you could sit on the bike to stop this but I reckon you will need both hands on the puller so not easy to guide the top loop into position.
Pulling downwards is not easy with a puller and using a a wood lever is awkward as you need to guide the loop over the peg.
Anyway, all I did was to squash a thin wall tube in a vice so it just slips over the stand peg and then squeeze the tube a bit more further along so the spring slips easily along it and off onto the peg. Using it is very easy as the tube is located securely on the peg and cannot slip off. With the bike on the centre stand, the tube is fitted on the peg (with the squashed oval profile in the vertical position) about 1cm. You then just lever down effortlessly with the long lever and the spring automatically slides along and onto the peg in one easy motion. You then remove the lever and move the spring back onto the groove of the peg. This is all done safely and without strain. Hopefully someone will find it works well.

Les