Can I change the density of troops within a front line?

[Sledjer]

it would be nice if I could make the front line specifically denser in a couple provinces, either because the AI seems to completely ignore supply limits when arranging a front line, or to break the enemy front line at a point. If I move more troops to a province than the AI likes though, it immediately railroads them off. Is there a way to tell troops to stay at a point on the front line?

 

[Eh up me duck]

Not directly. If it's very important you'll be better off creating a second army and manually control them in order to bolster your defences.

 

[Anaraxes]

How about not assigning them to the front line, but just manually moving them to where you want them to stay?

Increased density to break a line is probably better handled with two armies. One army can be your pinpoint breakthrough army (perhaps relatively small) while the other gets the "general advance" order to pin the defenders.