ComboBox: Make only some items to appear in dropdown list

Hello there!

Depending conditions I am able to setup, I want to have only some items to appear in dropdown list.

Example:

"label 1", "data 1"
"label 2", "data 2"
"label 3", "data 3"
"label 4", "data 4"
"label 5", "data 5"
"label 6", "data 6"
"label 7", "data 7"
"label 8", "data 8"
"label 9", "data 9"


I just want to display in the dropdown list:

"label 1", "data 1"
"label 5", "data 5"
"label 6", "data 6"
"label 8", "data 8"

i.e. the following are discarded

"label 2", "data 2"
"label 3", "data 3"
"label 4", "data 4"
"label 7", "data 7"
"label 9", "data 9"

Is this possible?
I hope so... It will be very valuable for me!

Thanks in advance for any help.