This very initialism is invariable.
However, there are some acronyms like ЗАГС, БОМЖ, ТЭН etc. which do decline as any other noun would, and in fact many Russian speakers are unaware those are initialisms.
This is more common for initialisms which would have been masculine if they were nouns, however, ЧК used to decline as well in early XX century (забрали в чеку, арестован чекой etc.), and the acronym з/к gave birth to the (masculine) word зек "inmate".
There is even a vernacular word касемсот "a heavy tractor", which originates from К-700, a heavy tractor manufactured in Leningrad.
It declines and is in every other way treated as a noun, you can find ads saying продам касемсот модели К-701.