I think this could prove very complicated, since you could accidentally make thousands of expressions invalid in your project, if you did a find-replace that produced invalid syntax. There would have to be some way to prevent that, and that may in turn prove sufficiently limiting that the feature doesn't do what you want it to any more.
Find-replace is also notoriously error prone - for example if you do a naive text-based find and replace for "text" with "label", and buried somewhere in thousands of events you have some dialog shown in game saying something like "In the right context we could...", that will also update to "In the right conlabel we could...". Now you've mangled a bunch of your game's dialogue in hard-to-find ways that will only show up after hours of playtesting. This is such a common problem that whenever I want to do find-replace myself in Construct's code, I actually just do a find, and manually update all the results so I don't end up making that type of mistake. So I would suggest a similar approach in Construct is wise - and you can already do it that way.
For the most part, if you rename something in the editor, like an object name, it automatically updates all its references in the rest of the project. So it kind of exists in that form already.