Okay, that wasn't too bad. However, I don't think you need to repack it into DAT. Here are some steps for those having trouble:
Step1 - Extract etc.dat
Step2 - Copy the etc folder into your RE4 directory
Step3 - Find the core.dat file within the etc folder
Step4- Right click on core.dat, go to properties, and uncheck "Read only" and hit apply.
Step5- Put the laser tool in your RE4 directory
Step6- Run the tool
-----------
NOTE: The laser tool must be in your re4 directory...
This is what worked for me hopefully it will work for you. Maybe St.Vampyre, should pack the etc folder with the core.dat in his release.
Anyway, good mod! Simply amazing work!