Changing the icon for the .lab files requires a registry change. Assuming you have installed Labeler to the default directory, you can download and extract https://dl.waspbarcode.com/wasp/supportfiles/Labelerv6IconAssociation.zip then double click LabelerIcon64.reg or LabelerIcon32.reg, depending on whether you have 64 bit or 32 bit version of Windows. If your copy of Labeler was installed to a non-standard directory, edit either of the .reg files with Notepad and replace the path with your Labeler path, then double click the file to run it.

After the file has been run, you will need to restart Windows for it to refresh the icon.