Inject in a specific place

[Osama Muhammed]

Hey guys, I'm sick of this, Whenever i think of some script to make this thing stops me, I need an option that lets me select where to inject my written Javascript ? i know theres a run-at option but its only top and bottom

Sometimes theres a function in middle and i want to edit it but the thing is. the function gets called write after its written so when i try to inject on top, it wont work because when it comes to the middle function it will override my javascript, and when i try to inject on bottom it will be useless cus the function was already called, 

Any solution for this ?

an example, option that asks me what line to inject in,

so lets say the original function is on line 10 and its fired on line 11

i want to inject mine between them both like in line 11 then the function call begins