I am unaware of a command to systematically convert guides between page-only and drawing board guides without direct users interaction with the guide itself. That doesn't mean one doesn't exist, merely that I'm completely unaware of such a command.
The only way I know to covert existing guides is to click them. As you know, were you release makes all the difference. You can click a page-only guide, drag the mouse outside the page and release, then it's a drawing board guide (or see the hot key below for page-only guides). And vice versa - click a drawing board guide, have the cursor over the page, and release, it becomes a page-only guide.
I am aware this does not solve the "Damn! I moved that 2pts" issue. Which is annoying to me as well.
When dragging guides, if you are letting go on the page, holding Command/Ctrl when you release the guide will make it a drawing board guide, as opposed to a page-only guide. You'll see it extend as soon as you hold Command/Ctrl. I don't think there's a command when dragging and creating a drawing board guide to restrict it to the page though.
And holding Option/Alt key while dragging a guide will rotate the guide 90°, making a horizontal drag create a vertical guide and vice versa.