Posting a screengrab of what you want exactly would help.

It is doable to grow long grass in the hair room.

But you know?
Once the grass is grown and simmed, you can manipulate the grass with any other tool.

Grow the grass in the hair room.

Then you can manipulate it with windfroce, or with magnets, or with the morphing tool.

I would have to know what you exactly want before going deeper?

That is why screengrabs would help.

Fresh cut grass can be made with a displacement map and a noice node.
Long grass can be made in the hair room.

Afterwards it is testing to get the result you need.

A hair room and or a cloth room can calculate dynamics and collisions, but to make the long grass being pushed out of the way when a figure is walking through it takes some testing.

ha-ha-ha-
What you CAN do.

Build your grass scene INVERTED..... !!!!! Upside down.
Grow the grass on a plate prop, save simmed hair/grass into library.
Load the grass prop and invert it back into normal position.
Then manipulate grass with magnets or morph tool  as your figure walks throug it?

This INVERTED trick is also used to keep panty's not falling off a figure during a cloth sim.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!