Besy soltuion for you would be open the call center if the agents are logged in and if they are not do not open the script.
To change a bolen varibale at the beginning of the script identify the ANI and if it some thing which is in the list then allow then press 1 to put the bolen value to 1 & 0 to put it to 0.
that way only authorized people will be able to change it
p.s: rate the p[ost if it helps