Yes I definitely recommend a spokeshave for fine tuning the stringer and not tearing the foam. But, tear-outs are a common occurance with EPS foam and there is no way around it. There are 2 ways to remedy tear-outs
1. after shaping spread a thin layer of lightweight spackle over the blank to fill in the holes - or you can use an epoxy / Q-cell slurry which gives the board more strength but increases weight a bit.
2. Use various sanding screens and foam shaping pad to close up the tear outs. Each progressive sanding screen grit will shave the EPS bead down and not tear. We use up to 320 grit to close them all up...
Please note the quality of the foam has a lot to do with it... make sure the blank in at least 2# density. Also, sharp tools and shaping a little slower help reduce tearouts.
I have used Micro-planes before and in my option they do not take enough foam away. Takes forever to get the shape you want.
We developed PRO-TOOLS to aggressively and efficiently shape EPS foam. They do cause a little tearing which is normal but finishing the shape with spackle or sanding screen makes the board look like a polyurethane blank.