By "designer tips" do you mean tips that are as clear as glass, with nail art already applied to them?
And is this particular brand "pre-etched"? (Not all are)
If you answer yes to both questions above, there is no need to 'blend' the tip. 1st off, you'd blend the design right off

2nd, as they are clear as glass, no demarcation should show (assuming you don't apply too much adhesive that squeezes out along the seam. If you do, wipe it away immediately before moving to the next nail).
So, you simply prep nails, size & apply tips, trim length and apply bonder/primer and product as required for your system.
If they are not 'pre-etched', then use a yellow/gold buffing block (or lighter grit) to sweep 2 or 3 times
LIGHTLY across the tip.
Just barely. Just enough to say that you did it. Any more than that, and the design will come off.
Then proceed as usual. The point is not to blend the tip but to rough up the surface SLIGHTLY so that the product will adhere.
hth's