New line in BEx for known master data only

Hello,

I have Planning Query in BEx. When I create a new line, I am able to put any value of characteristic. If it doesn't exist, it will be created (for example 0PLANT = XXXX). The problem is, I want to switch off the possibility to create new lines for values of unknown characteristics. Only new lines for master data already available should be possible. user should be prevented to create new Plants, Materials, regions etc. Any hint?

Cheers,

A.