Yes!
Those dialog controls are always tricky to modify.
So the correct answer should have been,
"sorry you can not do that but,..."
I have another approach that may help.
I customized a non-dialog checkbox by copying the images from the dialog version and pasted them into the non-dialog version.
Since it is not a dialog type, LV does not "fix" it for me when I re-open.
I hope the attached is more helpful than my previous image.
Ben