To add custom headers to several / to all requests of the given scenario

Use case:

 

The scenario contains x pages. Each page contains y requests.
E.g. I need to add a custom header to each first request on the each page.

 

The idea is to make an option to edit specific requests in a certain way. 

Something like this:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On the image above I want to select Requests 189, 191, 192 and then update them, adding some specific header: Parameter / Value