How to cast Thorn without leaving ennemy target

Hi guys. I would like to put in my feral macro the use of Thorn (https://fr.wowhead.com/spell=236696/épines);

I would like to do is using it in raid. I would like to keep the ennemy target as target, and cast Thorn on active tank (so on ennemy target) without having to set active tank as focus (because as you know, the tank switch).

Is it possible?

Have a nice day

You can make a macro that switches your focus target quickly I have mine set to Q; using the blizzard UI without GSE as follows

/tar [@mouseover,exists]
/focus
/cast [@focus,help,nodead] Thorns

Or possibly a target of target variation

/script TargetUnit(“targettarget”)
/script CastSpellByName(“Thorns”)

Or

/cast [@targettarget] Thorns

Or

/cast [help][@targettarget,help] Thorns

I have not tested the last 2 target of target variations but I use a similar focus switch macro made by KHIT (lazyturtle) for lifebloom on retail