How can I edit the original Myst app so that it no longer requires the CD to play? I just discovered SheepShaver and I'm mindblowingly excited!

I got all my old Mac games out of storage and began to install all of them.

A trick that I learned awhile ago for making playing games on OS X is to simply make a disk image of the CD and then mount that when I want to play.

I read about a 'technique' for making Riven play without the Disks which is essentially to edit the riven.cfg file that comes with the install to no longer point to the CDs but instead to point to local directories. I figured something like this should be possible with Myst.

Turns the Myst app looks to be some sort of Hypercard script. I made what I felt was a logical edit to it which was removing all Myst: prefixes that I could find in the file but that makes the app inoperable. I figured someone else would know how to do this better than me.

Thoughts?
You could make a disk image of the Myst CD and mount that for sheepshaver.

The original Myst for Mac was indeed an enormous Hypercard script. The Myst: prefixes you refer to are the program referencing the Myst CD. Classic Mac OS used colons as directory delimiters, so the file paths would appear as Myst:Images:Clocktower.jpg in Classic Mac OS or /Volumes/Myst/Images/Clocktower.jpg in OS X. You'll need to rewrite the paths to point to some local file directory. 

Say you installed the Myst app in an Applications folder at the root of the system disk. (This is the OS X location and is not correct or typical for Classic Mac OS, but I have no idea where Classic users stuck apps, so I'll use OS X conventions as a fallback.) This would be /Applications in OS X, so it's Macintosh HD:Applications in Classic (assuming, of course, that you haven't renamed the boot disk). Drag the contents of the Myst CD to a Myst folder on the root level of the boot disk (Macintosh HD:Myst:). Then you can re-point all the file paths in Myst to that directory.

Programming note: I'm on Windows at work at the moment, so I've no way to test this immediately. Caveat emptor, but this ought to work.