Don't think so since you can't use command calls in reactors, and I don't know of any way to use a script without a call to the 'script' command. If you can figure out a way to issue the script without the command, then yes.
With that said, you might not need a reactor. You maybe just want to use the 's:startup'. You will want to use this as it fires after Acad loads all it's stuff, that way you can use a command in the call backs. All you need to do is test the variable 'ctab' and then issue the right script call. I don't use the 's:startup' so I'm not sure how one would go about using it, but I have seen this stated as a way to do stuff like this.
