How can I spread a modulated signal over walsh code
That's right, you can do spread using the kroon function, but be careful what you spread is not the data, it's the whole possibilities of data which is mod.The data is one of them, which is either, 0.7+0.7i or 0.7-0.7i ...etc. 

then you should know how you can do despread in the receiver side too. 

Good luck