Incenjucar
Legend
...or kind of like using a double weapon and smacking someone with an axe head and expecting it to be treated as a spear (which it is.)
I can buy something like Brutal not carrying over (maybe.) I can see the reasoning as to why it wouldn't; however -to my knowledge- there's nothing which prevents a weapon in the Improvised Weapon Group from having the brutal property. Still, I lean toward Brutal probably not carrying over.
However, the change in size and change to being improvised would -as best I can tell- not have any effect on the magical enchantment which is already on the item.
Improvised weapons have very specific statistics. You follow those statistics and no others.
I'm not sure, but I think that you only get to use magic item properties when using an item in a normal fashion.