I don't really know how such "bug" could be found...
If I remember how some vic hardware bugs are used -they basically change some register or registers at the right time during a rasterline... or something like that... So I guess on the nick it could be also something similar? Although the margin registers are used only at the horizontal blanking and changing them in the middle of a line won't change anything. Oh and will nick know about the lpt change automatically?
Although many useful things can be done by Nick "normally" - like repeating lines, "opening borders", rasterbars, scroll(?).
And how easy it is to make a vertical rasterbars "demo"
and how little code it needs - one line of graphics stretched to fill the entire scrren and animate this one line.;P
But being able (for example) to somehow scroll the screen by halfbytes and offset margins by one byte instead of two would be great...
Also I don't know what you could achieve with changing some modline parameters in the middle of a line...