Cutting through that foam for pipe/wiring upgrades might be a bit messy but certainly is easier than cutting through 150 year old lumber. Go find a cheap "oscillating multi-tool"...or find a cheap fillet knife! As for historic integrity, costs more but there are ways to preserve your wood from foam if you want to bother but IMHO you will most likely lose some of the benefits of foam in terms of energy efficiency (probably not much)...thinking...
I hear ya...and it is a barn after all. We're not expecting it to be warm like a residence, but we also don't want our employees filing workman's comp for frost bite! The challenge in the attached barn was actually finding the pex inside the foam and tracing runs. I would do it differently next time.