If you are so well informed, post your reference, what's the problem?
Half-arse answers is not being informative.
I can only state what the Gun shops advised back before that time, they could not sell a gun in the name of someone with a temporary residency card. So, somewhere the law must have changed if as you state it can be done now.
My reference is the Ley #36 Sobre Comercio, Porte y Tenencia de Armas. Read it completely in Spanish.
The status of the first license was temporary. The plastic itself was the same, but the license number was in a different format/number of digits. When I renewed it next year, it became permanent.
The law says that temporary residents can obtain the license, but in case if they leave the country, they have to deposit the firearm to some special storage at MIP. But if you read the law completely, you will be surprised that in the another paragraph it says the same for all permanent license holders too... it was the general rule for everybody who has a gun, but it was never enforced, never.
By the way.... Two or three gun shops said to me that they can not sell a gun in the name of someone with a temporary residency card, the same like they said to you. Finally, I walked into another gun shop, they said no problem if I pay for a new gun and license. I bought the gun and got my license in a couple of weeks.
P.S. The Law was not changed since 1965. There were some documents issued by SEIP (MIP) regarding prohibiting the carrying of firearms in places that sell alcohol, the famous idiotic prohibition of carrying firearms in December some years ago, the restriction of import signed by Leonel, etc, but this has nothing to do with the original Law, it's still the same.