Canary Islands, Zone 11B.
I doubt that junipers will be dormant in that climate for many months if at all. I'd be inclined to try some grafts to see what happens.
I've certainly had success with out of season pine grafts through summer. Biggest problem is keeping the scions hydrated in hot, dry weather.
Cuttings are much easier than grafting and you can use rooted cuttings to approach graft if you need to graft. Approach graft is a bit slower but far more reliable for beginners than grafting scions.