Update / install ionic not globaly for testing (on MAC)

hi folks,

i have the following problem. i have multiple apps build in ionic 3 and it works fine but now i have build a new app in ionic 4 for testing it. i developed the app on another windows computer so i still can maintenance my older apps for ionic 3.
now i only have one mac and want to try ionic 4 also on ios with xcode. here is where i need a localy ionic 4 installation and no globally - so i am still able to maintenance and build the ionic 3 apps like before.

i found this thread here but i dont really get it…
can someone make a clear instruction how to? would be very nice and i think it will also be very usefull for other ppl who just want to make test build before globally update the framework.