I'm just wondering if anyone knows of a way to add an expression to any animatable parameter in ae which would link it to the value of a cell in a spreadsheet?
I know about 'templater' from ae scripts but I'm not sure if this is this flexible...
You can't do any such thing. While there's a rough and rudimentary file method, it has no inherent intelligence and only reads small amouints of text as code streams. If you wanted to address specific parts of the file, you'd have to implement a complete structure parser inside the expression itself and then there's exactly zero benefit in using this method at all. It would be slow as molasses in winter. You realyl need to think of other ways, which could include editing text layers and converting strings to values for instance. Or indeed you need to spend time and money on using scripts and have them update your comps every time they run...
Ok thanks for the info.