It is accepted technique to use BOILED Linseed oil over acrylics. I like to let them 'cure' beforehand, but have done it fairly quickly after painting. I haven't tried it on Pine, so you may want to test it first.
Most paintings I have seen mix the boiled linseed with a dark oil paint (such as raw umber, I believe) as a stain. Some use polyurethane on the face first to preserve the bright coloring of the face. Otherwise, it does get darker and looks more like an antique, a nice finish for most pieces.
Read the directions ( Â*

) for using boiled linseed since it is highly combustible.