At this point your existing fluid is probably fairly loaded with friction material etc. This is most likely causing a fairly substantial pressure drop across the filter. Eventually the limited fluid flow will cause it's own issues. However a simple drain and refill will only change approx 30% of the fluid volume. So if you change it and you probably should, then in order to have fairly clean fluid you will need to plan on changing the fluid about 5 times in succession. Even then you will probably end up with approx 25% dirty fluid circulating. The problem is the torque converter holds around 11 qts of fluid and there is no way to get it out short of pulling the trans and torque converter. In short you will dilute 30% of the fluid 5 times.
Clutch packs might not like it but your valve body is going to love it. More info in the thread attached.
http://986forum.com/forums/general-discussions/61760-tiptronic-transmission-oil-change.html