The majority of plugs we buy today don't have the removable tip.If you change the plug you can use the same boot,just unscrew the tip on your new plug.
I've never seen a spark plug that doesn't have a screw on tip. I'd like to
know what brand doesn't. As far as reliability, the best, most durable plugs
are made by NGK or Bosch without a doubt.
I've worked on motorcycles and car engines for over 40 years, and yes,
they were all under a shelter, because I have enough sense to stay out
of the rain! ALL of the plugs unscrew at the top, that's how the porcelain
top is assembled. Put those "non removable tops" in a vice and learn sumthin'