From a standard mms, I don't believe you can. ( it's this way for every phone on the market for standard mms that aren't imessage or hangouts etc)
The best solution would probably be in changing your messaging app. there probably are some messaging apps that allow you to mute specific conversations so you don't get notifications for them even though you're still included and will get the messages
Another option is to ask the group to remove you from their message thread ( they would have to start another mms thread)
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