Adding lime juice to green curry paste and heating
Lime juice is one of the components of green curry.  The acid from the lime juice macerates some of the other ingredients and wakens up some other flavors. If you don't add it as part of the paste preparation, then you aren't cooking with Green Curry.

If you add the lime juice in the end, you will have a very different result, mostly that of a dish that tastes like it was sprinkled with lime juice before served.