What to do when extrapoling and replacing part of a model?

Hi

I made a change to part of a model in a very tight spot
I built the amendment outside on the side of my main model

1st I copy pasted the area I wanted to change
2. I made the changes and made it into a group
3 Now when I want to bring it in again
do i NEED to delete every line of the old part of the model
or when I bring in the new group and explode it will it
take the place of the previous lines + the new parts
OR will I end up with two of the same lines in the same place riding each other?

Thank you.

I believe that the old parts have to be deleted before you bring in the changed part. Are the old part(s) groups or components? If so they should be easy to delete. I would avoid exploding if at all possible.

Thank you. Yes they were a group but to bring in the change I had to open the group
Thanks for your help