Precautions to be taken while changing the Query read mode in PED system

Dear Experts,

I got a task to change the Query Read mode for more No. of queries in Production system directly itself.

Request you to let me what are the steps to be followed/precautions to be taken while changing the Query Read mode in PED.

one more doubt regarding this.....If i plan to change the Read mode of Query say Q1, how can i come to know weather the Q1 is executing or not executing by that time.

Thanks in advance for valuable response.

Thanks & Regards,

Ramesh - Kumar