You can trim it in summer to maintain shape and height but not prune hard no.

Old plants cut back to stumps sometimes don't sprout again. If it's a size issue, I would cut about one third of the longest branches back to side branches at least 1/4 as thick as the branch you are cutting. Repeat with another third the next year, and again the year after. At the same time, be ready to thin out excess sprouts so that the crown doesn't become a tangle. Here, we would seal all the cut ends to keep out the flat-head borers, but I don't know if you have the equivalent there.

Fortunately not, Tugbrethil - one of the advantages of a temperate climate is less nasties. On the other hand, we probably get more things caused by damp.

Yeah, preventing heart rot and the like must be an adventure!