Primary Zelda Hacking

While there are four overworld maps with a set of rooms from 00 to FF each, all the dungeons and indoor rooms share one set of values from 00 to FF.

I know i can rearrange the rooms within one Map Group.

But is it possible to rearrange the map groups themselves?
For example, instead of having a one-floored Spirit's Grave with one map group of 21 rooms, could i split these up into two floors with 10 rooms each?

I'm just wondering because i had the idea of making a past version of Moonlit Grotto (similar to the Mermaid's Cave):

(http://img545.imageshack.us/img545/2763/alternatemoonlitgrottop.jpg)

(Currently i was just playing around with the map editor, i know i have to be careful with the right border. Writing the script is likely quite a mess as well: only the past version should allow inserting the eyes, the present version has to get updated once the eyes in the past version are inserted, and you normally only have one item of that kind as well, so you won't be able to carry two of these at once...)

Of course you can. However, the minimap will not look right. You'd be using Level 2 B1 for another floor of Level 1, just for example.

In a similar vein, my hack consists of almost entirely single floor dungeons (likely due to the limitations of the original GameBoy).  Is there any way I can remove the other floors from the map or repurpose them as a different time?