iMessage refuses to let me group text to an alternate number. How to fix this?

[EugW]

My sister has a Toronto phone number. My niece also has a Toronto phone number. I have them in a group message thread.
However, my sister now has a Mexico phone number and gets her iMessages there.

Now if I create a group text with my sister's Mexico number and my niece's Toronto number, iMessage automatically changes the Mexico number to the Toronto number and the text to her fails. I tried on both Monterey and iOS 15, and get the same result. It's frickin' aggravating.

Even if I manually type my sister's Mexico number in to create a new group text, it automatically changes it to the Toronto number. What doofus thought this was a good idea?

Is there any way to fix this?

 

[now i see it]

As a hack workaround, create two contacts of your sister who has the two numbers. MexSis and TorSis. Then you can choose one of those numbers depending on what you want.

 

[EugW]

As a hack workaround, create two contacts of your sister who has the two numbers. MexSis and TorSis. Then you can choose one of those numbers depending on what you want.

Thanks.

What I eventually ended up doing for a workaround is to delete her Mexico number from her contact info. Then I rebooted* and then started a new group text with her Mexico number. Then I added her Mexico number back to her contact info.

That worked, and after I updated her contact info, iOS merged the new iMessage thread back to the original iMessage thread, but now with the new Mexico number. Not sure why it decided to merge it, but that's what it did.

*I had to do the reboot because it didn't work initially. Even though I had already deleted her Mexico number from her contact info, the behaviour was still the same as before. Maybe rebooting the machine forced updating of any caching in iCloud or something?

Why it doesn't allow two different threads makes no sense to me. Your method makes a lot of sense, but shouldn't be necessary. Tons of people have more than one phone number (eg. home cell vs business cell), and it shouldn't require two different contact entries just to make use of more than one phone number for a person in iMessage.