I guess they have the new rules this year. cause I was in TGS last few years and I also saw some cosplayers with prop.
This is the offical site of TGS and the link for cosplay is down in the righthand side corner. only in Japanese site though...
Anyway there will be some stuff checking each cosplayer`s costume before they exit the dressing room, and they will take away any accessary or prop that does not fit the rules. troublesome.
Maybe there is someway to bring the prop? Maybe I will ask my friend to hold on my prop and handed it me after I exit the changing room?