Can I use the black Fca external cable for a long internal run through a building?

Do not treat the external sheath as an upgrade over the indoor cables. The black PE products are CPR Fca and are sold for external use; the indoor LSZH products exist because internal installations have different fire-performance requirements.

Where a route passes from outside into a building, the internal section has to comply with the project's fire and cabling requirements. The sensible design is to choose the cable for each environment rather than letting a convenient drum dictate the fire strategy.