Yes the long needle carb will tune quite differently to the shorter needle carb on your 7 port.
The trick is make sure you have the HSN set rich enough. Then you just tune with the LSN only. Set the HSN to .25 in from flush and leave it there. Now tune with the LSN until you have it running good. If it is a little rich at the very top of the rev range (say the last 20%), then tweak the HSN in a little, like 1/16 to 1/8 of a turn to get that last 20% of the rev range perfect.
Now you are tuned in, any changes due to weather etc you make with the LSN only.
Because the longer LSN stays in the spray bar throughout the entire rev range, it is neccessary to have the HSN set rich enough to pass enough fuel past the LSN needle tip (especially at full throttle). Unlike other carbs where the LSN works up to say 1/2 throttle then the HSN works after this up to full throttle, in the long needle carb the LSN regulates the fuel from idle right up to full revs. All the HSN is doing is acting like a tap, to ensure there is enough fuel available, no matter where the LSN is situated.
If you get any lean bogging (especially as the tank level gets down) it's a sure bet that the HSN is too lean on this sort of carb. Depending on fuel and pipe types, you may need to run the HSN flush or above flush to get it working spot on. I found that around .25 turns in worked for me with the 0801 or 2047 pipe. I have changed both my motors to the shorter needle and am loving it. I don't find any negative effects on performance or economy, but they are easier to tune in general.