Selection variables (table TVARV)

When scheduling background jobs I was recommended to use selection variables for the fields reffering to different dates. However, some of the fields in reports I want to schedule does not have the DATE format (instead they have e.g. period and year) and I am restricted to selection variables in table TVARV. So my question:

Is there any way to have the values of the variant variables in table TVARV change automatically (e.g. have one field that holds the current month).

Many thanks in advance

/Martin