I guess everyone knows that Japanese swords were and are re-tempered, a process which is called „saiha“ (再刃) or „yaki-naoshi“ (焼き直し). But there is also a way, even a bit more difficult, to re-temper just the bôshi, and this process is called „yakitsugi-bôshi“ (焼継ぎ帽子, lit. „patched bôshi“). Usually it can be detected by a considerably weaker nioiguchi from where the smith decided to have his re-tempering started. Apart from that, a mizukage might appear just like at the ha-machi at a full yaki-naoshi. But a yakitsugi-bôshi is more rare than a complete saiha and I haven´t seen a blade showing this feature so far. However, it was not uncommon in the past when swords were actually used. That means when a certain sword got damaged at the tip and it was decided that it is good enough to be used again on the battlefield, it is possible that the repairing smith suggested having only the concerned kissaki section re-tempered and not the entire blade.
Schematic oshigata of a yakitsugi-bôshi.
Another possibility to „add“ a new bôshi is by needling but this process called „kaki-bôshi“ (描き帽子, lit. „drawn bôshi“) is just of a cosmetical nature. Here the polisher is able to reconstruct the bôshi by adding small dents with a fine needle. In the light, these dents appear just like nioi and I can tell you, I have seen a needled bôshi and it is really hard to tell at a glance that it is cosmetic, i.e. that there is no hardened area present. When it is well done by the polisher, you have to take a really close look under the light to see the small needle punctures.