I can't answer the question other than to say that I have just contacted Casio to ask them how to fit the replacement watch strap they have sent me and they say either to take it to a local jeweller's or send the watch and the new strap back to Casio and they will do it. The necessary device needed to get the strap-retaining pin out of the watch (and then back again with the new strap) is not available, and anyway, they said, they would not recommend customers to try it!
Barclay Lawrence
June 2009