In order to read in a definition with certain parameters replaced by appropriate values I can use for example
Block[{a=1.1,b=2.2}, Get["file"]]
where "file" is a file containing the definitions (which contain a and b on the RHS). This works well and is fast. Now is there a way to do something similar if I want to replace a string. So basically, Block[{"string"="bla"},Get["file"]] (but then in a way that actually works of course).