Rule No. 1: Backup Tracks.bin or better the folder NetWorks\ .
The normal Editor in railworks cannot do that. and you do not need RWtools (maybe it is possible) - by principle you decompile the Tracks.bin with serz.exe to Tracks.xml and edit it.
Then you replace all entries for tracks with the tracks of your choice. The Problem is, that you often have to replace over several lines, as you have to replace provider and project, too. This can be done with a good texteditor like notepad++ or notepad2 or with the scripting language perl (i do it in perl, but if you have no clue about it then try it with an editor). You have to take care about capitalization. The entries for provider and project are case-sensitive, but the entries of the folders below the project and the name of the track have to be written in lowercase, even if they are uppercase.
You should create a trackrule or use a trackrule which includes the tracks your new tracks. So you have to change every rule in the Tracks.xml, too.
Finally you have to complile your new Tracks.xml back to Tracks.bin and hope that it worked.
When doing this work you have to be very acurate otherwise you won't see any result. Write down all the steps for yourself if you haven't done this yet. The tracks might not be lost but invisible. It's better in that case that you start by new with your backup.
Kris