"if CIO of all neighbor cells changes regularly how do i inform UEs about the latest CIO"
Typically operators configure the MRO algorithm to run during the OFF hours when there is no traffic. The MRO algorithm can be configured to run once a day or once a week for eg.
When the CIO changes, then the new CIO there can be 2 options :- a) Either tell all the UEs that the CIO changed by sending an rrc_recfg with measurement change
b) Inform only the new UEs about the new cio.
"b)" seems like a more easier to do option than inform all the UEs.