Add control on how Global Transforms are loaded/applied
Do you mean you want a way to add a global ast transformation from command line ?
Both issues show that the global AST transformation mechanism implemented so far is not easily customizable.
For my understanding, why do you need to add global transforms from command line ? Isn't the META-INF/services/org.codehaus.groovy.transform.ASTTransformation file sufficient ?
From the command-line, one could add a jar on the classpath with the meta-inf info, like suggested by CÚdric.