Help enumerating or converting dynamic {{topic}} to a specific string?

I use a Slackbot to send myself notifications for debugging and general logging the status of my house. I’m working on presence detection and I want to received notifications like “Bob just left”, “Bob just arrived”, and “Bob is now home”. But I have more than one person in the house to test on, so I also want to see “Bobilina just left”.

Currently I’m tracking “bob_pixel_phone” and “bobilina_iphone”, and in my Slack JSON I’m passing:

{"message":"{{topic}} home"}

which works at giving me “bob_pixel_phone home” and “bobilina_iphone home”.

Besides copy and pasting the entire presence detection flow for each person, how do I enumerate that “bob_pixel_phone” should actually turn into Bob and “bobilina_iphone” should turn into Bobilina?

Just had to use a Switch Node checking for each “bob_pixel_phone” / “bobilina_iphone” and connect each to a Change Node like this: