A primary action type is that shown in IT 0. A secondary action type is stored as IT 302. For example, when a person is hired, the first stage of hiring may just have non-value related infotypes e.g., IT 1, 2, 6, 16, etc; this would be performed by a HR admin person and would be a primary action type. The next stage could be payroll related with IT 7, 8, etc performed by a payroll admin person and would be a secondary action type. A secondary action type is stored in IT 302 and displayed in the bottom box of IT 0 of a pers.action type performed earlier.
I'd suggest that for confirmation, you can set it as a secondary action type. However this can not be executed on a single day as an independent action. You may reassign a person to another position with an action type. Then execute confirmation action. This will show the confirmation action as a secondary action in the IT 0 record for org re-assignment or any other action performed earlier.
In SPRO->Pers mgt->Pers admin->Customizing Procedures->Set up Personnel actions, select Personnel Action types (or in SM30 maintain T529A). For a secondary action type, tick the field P0000 Update infotype 0000 when executing an action. This is the check box after Date control column in T529A.
This will result in not creating a separate IT 0 record for this action type.