Rojak, you can change and top up for different flowers used. They use the normal roses for set up. So say you want to change to peony, hydrangeas etc, then you top up accordingly lor.
Top up amount of flowers during my time was like $80 per table, then stage was another few hundreds, change flowers another few hundreds etc.
We also wanted to add additional props like say i choose theme 1, then use certain items from theme 2 to add on, then top up again as consider on rental basis....
There are many ways of doing it.In the end we did not go for it cos it is not worth it.
Bottomline is this. For theme, you have to choose one. Then big items like stage, aisle, centre pieces must be from that theme. Small items like sash, table linen, flower type, flower colours, additional props or items from other themes can be changed or add on. All these are subjected to top up and additional costs accordingly.
This is my experience. The rules and regulation from the hotel might have changed. But if you want, no harm asking your coordinator regarding this.
However, be warned that it can get pretty messy and high in cost.
Best way of doing this is to add more flowers by topping up, change sash and table linen if needed.
Or else, the themes are already very nice by themselves. Only thing is the amount of flowers. But without top up, there are already pretty good.