You can update an Environment if you have only added objects to it, but not deleted anything. Only the new objects will be imported; the older objects (along with their cabling and track assignments) will remain in place.
Logic Pro offers several options for swapping the Environment of one MIDI setup with the Environment of another.
Choose Options > Import Environment > Update.
Do one of the following:
Choose Options > Import Environment > Replace by Port MIDI/Channel.
All objects in the destination project are replaced with objects that reference the same port and MIDI channel strip in the source project.
Choose Options > Import Environment > Replace by Name.
All objects in the destination project are replaced with objects of the same name in the source project.
Choose Options > Import Environment > Total Replace.
The destination project’s Environment is replaced completely with the source project’s Environment. If you use this option, you’ll have plenty of work to do, including reassigning main window tracks to objects, but sometimes it’s the only way.
Note: This complex task involves a lot of guesswork on the part of Logic Pro, and the results almost always require some manual fine-tuning on your part.