Airport Codes on FLight Plans

[topcat450]

Hi,

First of all apologise if this is wrong area to ask this...mods feel free to move it wherever...this is my colleagues problem:

I assume when filing a flight plan, you use the ICAO codes for airports?

So, what happens when the airport your going to no-longer has a code... it's been deleted? eg. KISM used to be Kissemee, FL, but speaking to ICAO this has been deleted.

Also when searching NOTAMS, if you can no longer search for KISM...what do you do?

I was a big confused as I thought the ICAO codes were pretty static but his evidence suggests otherwise.

Thanks

TC