Thanks for the interest in (Excel) .NetMap!
Undirected graphs will not display arrow heads (and several network metrics will be calculated differently) if the toggle for directed and undirected graphs is selected in the ribbon.
Skipping selected nodes is simple to do with a formula in the "Visibility" column. Try something like =IF(CellRef=Condition,1,0) to test if a cell meets a condition. If the condition is true, place a "1" in the cell, if the
condition is false, place a "0" in the cell. Any row with a Visibility = 0 will not be displayed.
Your request for a feature that could be called "Remove all non-selected nodes" is a good one and we will add it to the feature request list.