You're right again! I was a bit in a hurry yesterday...Unfortunately it won't work as it replaced the entire word abc|100°F instead of just 100°F. The regex matches everything before and including the first ddd°F instead of just the first ddd°F.
Eg if the string is:
abc def ghi 100°F 200°F 100°F
It would become:
xxx 200°F 100°F
Edit:
It's still doable without shell or JavaScript and I'm sure you can achieve it but it might take a longer macro. Would have been easier if Macrodroid had a replace first option too instead of replace all only.
This time I'll be necessary to add 2 other Text Manipulations like in my original (wrong) suggestion.