Hi @Srinivas2 :
Great suggestion!But currently Combox's option list does not support customization.If you need this feature, please refer to @PaulD1 ’s suggestions and post your suggestions on the ideal forum.
In addition, you can also use a combination of controls to achieve similar effects.Like this:

I'v made a test for your refernce:
1\Add a textInput box(TextInput5)
2\Add a 'Down' button and set it's OnSelect proeprty to:
UpdateContext({Var:!Var}) /*Var is my custom variable*/
3\Add a galelry(Gallery9)
Items
If(IsBlank(TextInput5.Text),["A","B","C","D"],Search(["A","B","C","D"],TextInput5.Text,"Value")) /*["A","B","C","D"] is my datasource*/
Visible
Var
Add a button into this gallery
OnSelect
If(ThisItem in MyChoice,Remove(MyChoice,ThisItem),Collect(MyChoice,ThisItem)) /*MyChoice is my custom collection*/
Text
If(ThisItem in MyChoice,"Delete","Save")
4\Add a horizontal gallery between TextInput5 and Gallery9
Items
MyChoice
Add a "X" button into this gallery
OnSelect
Remove(MyChoice,ThisItem)
In addition, if you want to use this combination in multiple places, you can also create a component.
Best Regards,
Bof