Not really sure, but check here 

https://www.geneve-parking.ch/fr/macarons-zones-bleues

Or just give them a call, or send them an email, and explain your situation

Fondation des Parkings
Carrefour de l'Etoile 1
Case postale 1775
1211 Genève 26
5ème étage P+R Etoile
Du lundi au vendredi, 8h00-16h30
Accueil téléphonique :
8h30-17h00
Tél. 022 827 44 90
Fax. 022 827 48 60
[email protected]

From https://www.geneve-parking.ch/sites/fdpg.ch/files/M%C3%A9mo%20DETA.pdf it looks like you need your car to be inmatriculated in the canton of Geneva:

Pour assurer une plus grande disponibilité de places de parking aux riverains, dorénavant, seuls les détenteurs de véhicules automobiles ayant une plaque d'immatriculation genevoise auront droit à un macaron "habitant". Cette restriction s’applique également aux macarons "Vieille-Ville".

Without being able to recite chapter and verse, the quotation above has always been my understanding of the concession.

Nope

tried this.

doesn't matter what reason they give you , but fundamentally it is against the law for a swiss resident to own a foreign immatriculated car.

I'm not sure if there is a period you are allowed to keep foreign plates, but i don't think so.

so the logic goes: applying for a macaron -> you live in geneve -> you must have swiss plates

According to this

https://en.comparis.ch/umzug-schweiz/migration/auto-umzug-schweiz

You're allowed to own/drive a foreign car in Switzerland for up to a year during which is must be registered. Macarons aren't cheap and also doesn't guarantee a space. You're probably better off renting garage space if you can find it near you

Macarons cost CHF 200 a year where as a private, space wether outside or in garage or "box" cost between CHF150 to CHF 300 a month. But yes it doesn't guarantee you will not have to drive around for 30mins trying to find a space depending on your neighborhood.