Bicycle Mechanics - Do I need a new headset?

Hi guys, new to this forum, hope you can help.

I have a specialized Tarmac comp 2009, I am trying to lower the front end to get mire aero. I have a few spacers above the stem and a 25mm cone shaped spacer below the stem, can I replace this spacer. LBS has indicated that it's part of the headset and I would need to change headset for a lower profile one.

Is this correct?

..I have a specialized Tarmac comp 2009, I am trying to lower the front end to get mire aero. I have a few spacers above the stem and a 25mm cone shaped spacer below the stem, can I replace this spacer. LBS has indicated that it's part of the headset and I would need to change headset for a lower profile one. It might be basically another spacer, but one with a bit of shape to merge better with the top bearing race. If that is the case you should be OK to remove it. But unless you are ready to cut down the steerer you need to add something of the corresponding height above the stem to set bearing preload.

Two things:
1) While being aero does have its merits, being able to breathe and see the road is more important. Assuming your bike is sized correctly you're setting it up rather oddly.
2) it is not advisable to ride "permanently" with a lot of spacers on top of the stem. Structurally it's a non-issue, but it poses a certain risk in case of an accident.

depending on the design the cone piece can be removed and regular spacers put on top . the cartridge bearing may be more exposed to the elements

The cone does the job of a headset cap and a spacer. Depending on what headset you have you may be able to replace it with a lower profile cap.