I have changed the ferrofluid in my tweeters. The ease or difficulty in doing so depends entirely on how hard or easy it is to dissemble the tweeters. It turns out in my case it was easy to dissemble to tweeter to be able to get to the channel where you wipe out what's left of the old ferrofluid and add the new.
Personally, with nicer speakers like yours I would just send the tweeters to Millersound and have him do the work. I'm sure it would be quick turnaround (guessing days) and very reasonable and Bill is great to deal with.
Regarding "ferrofluid", from the net:
"Ferrofluid cools down the speaker coils which are susceptible to extreme heat. Ferrofluid transfers and dissipates the thermal energy produced by the strong vibration of the moving driver. As magnets increase in temperature, they lose some of their power."