I’m not exactly sure if you mean in a single consecutive period of time, or if you mean on and off over something like days with the only place you tickle them being in that one spot. If the former, many people do get noticeably desensitized, and some don’t. If you meant the latter, That one is harder to answer with confidence. I personally don’t feel that it would cause less ticklishness for most people, but it probably depends upon which dimensions of ticklishness are most at play for that individual. I tickle my wife all over when we have time to dedicate to full sessions, but I tickle her in a few of the same easily accessible spots virtually everyday. If anything, I think I've only observed her becoming more ticklish over time with me doing this. I can very easily imagine another person having a different adaptive response to that kind of thing where they no longer register it as a threatening touch that makes them feel ticklish. A lot of being ticklish is psychological, so how someone adapts (or doesn't) will heavily depend upon their unique psychological processing over time.
