Variable substitution can be used in Code Templates (using &&) which displays the variable substitution dialog before pasting the template.
This dialog allows to [Cancel] but this only affects the substitution. The template is still pasted afterwards.
Fixed in next beta.
I expect that someone somewhere relied on Cancel to insert the template with substitution variable intact so that it prompts when running the script instead. Hmmm. Well, I’ve made it cancel insertion on ESC so we’ll see how this plays out, but it may need to be changed back.