Well, maybe. The problem I find with this type of conversion is that the 25 pair is often looped to many locations. The 1A2 phones are all bridged on the same pairs whereas modern systems like the Partner need separate pairs run from every phone back to the KSU.
Certainly 25 pair that is looped can be made to do that but don't expect to just plug a 259A into each Amphenol. You will have to cut the Amphenols off and use a regular jack wired to the correct two pairs of the 25 pair after you make the proper arrangements at the other end.
I doubt that there is any need to rewire, but whoever is going to do it needs to know what they are doing. It's not plug and play.
-Hal
