Both cases occur in industry. The parts that only go through additional testing (radiation lot acceptance testing aka RLAT) are commonly sold as “radiation tolerant”. Parts that undergo hardening via design/manufacturing changes are often branded “radiation hardened”. In either case though, the available part portfolio is much smaller than commercial. Further increasing cost is that these parts are often geared for military/aerospace so have expanded temperature ranges, stricter qc, weird package types, etc.