And now that I've looked I can remember looking at this a while back..
The information displayed in the profile activity is obtained via Search. The search index discards html content from the post so there is nothing within the content that I can check for:
there won't be any <a> tags, or URLS, only the plain text (ie the word Google, as opposed to https://www.google.com for the following link: Google)
there won't be any <img> tags
there won't be any <blockquote> tags.
In short, there is nothing within the content that I can check for and remove as it is just text. And with that in mind, the only option available is to perform a full replacement of the content, like I do with the 'Hide All Content' option in the application. Even then, I may not be able to even do that as the data appears to be protected so I may not be able to manipulate it.
What I am going to try to do:
Add a 'Search' option in the "Where?" setting, disabled by default.
Add a 'Search' tab, with the following settings:
"Hide from" being a group listing
"Replacement content to display" being a plain text field which can be populated with the replacement text to be displayed
Replace the content of the item entirely for display (dependent on topic or record location - but I may or may not be able to differentiate between a topic's first post and its replies, or a database record and its comments)