Let's say we have a necromancer. They build an item with a ReCo enchantment that animates a corpse and has it respond to the commands of the person who activated the item. The item is a collar or something that you put on the corpse.
The necromancer takes an apprentice. The necromancer wants their apprentice to be able to order around their zombie, but doesn't want to necessarily give up their own control either. They want both their apprentice and themselves to control the zombie simultaneously. They're hoping for a formulaic spell to solve their issue, if possible.
Is this something ReVi or Re(Mu)Vi or some other combination of Arts could reasonably be extrapolated to do within the current boundaries of Hermetic magic?
I'm not looking for a RAW answer, just subjective interpretations, anecdotal evidence, and wild, sybaritic masturbation if possible.
The apprentice will definitely need a magical item to control a zombie, the master probably knows the spell. So the apprentice can keep the item, whereas the master cast a spell when needed.
Handling control of spell, per rule, requires either Mutantes Hermetic virtue (Mercere specific virtue), or learning the Tethered mastering ability for a specific spell.
These are the canon alternatives. Can the master convinced a Mercere mage to teach him the zombie spell with Tethered master ability ?
There is the guideline from HP p97-98: MuVi Passing the Reign of Form.
The level of the affected spell must be less than the level +1 magnitude of Passing the Reins of (Form). But it can only be cast when the first spell is cast, not once the spell is in effect. So it would need to be something much more powerful to hand over the control of a spell once it has taken effect.
You also have to keep in mind that inventing such spell would allow any mage with the proper spell to steal the control of another spell - including lasting spell like Aegis...
Once you have the control of spell, it is easier to cancel/suppress it.
Be careful with the MuVi approach if you try that. (Don't know what was deleted.) MuVi must be cast as the spell is cast, and the canonical method will therefore only transfer control initially rather than allowing repeated transfers of control. You might work out another MuVi guideline for repeated transfers with your troupe, which should be notably more difficult than the single initial transfer.