Take at least a front and profile picture of yourself wearing the hat you want to mod. Add vector traces of the spikes over them with different colors.

This can be done in Adobe Illustrator or Inkscape (free).

Drop your vector art in an A4 canvas and scale the biggest one according to the chess pattern.

Print the sheet without margins and at 100%. Check dimensions.

Roll some klean klay on a ceramic tile to get an even thickness of approx 1cm.

With a cutter, cut out as much spikes as you can, leaving enough clay on the edges to have a solid mold.

The edges need to be sharp and corners clean. The tile has to be clean and slick (?).

Here the lower right edge is too thin and was only used for the purpose of the picture.

There is no need to add much pigment, a small blob will do for one spike.

Leave some on the borders to ease unmolding.

Poke bubbles.

Peel of the spike from a border, making sure the latex is dry underneath.

If it's still sticky, put it firmly back in place and let it dry a few more hours.

The color will be lighter underneath because the ammonia didn't completly evaporate.

This side has to be left to dry an hour to make sure there's no remaining liquid latex traped in between the coats.

Cut a few slits in the base of it.

This will allow the hot glue to get more grip since the latex is sometimes too slick for it.

Repeat these steps for all the spikes.

It can be done quickly if the you can make 3 or 4 spikes with the same clay mold (It took 2 days to make 7 different spikes).

Metal clips (40cm of 1mm² inox wire).

Solder extremities.

The left and right sides need to be long enough to provide an "horizontal base" for the spike.

Glue to hat according to vector art.

Make sure the clips are tight enough to hold the spikes, or at least to hold them straight when you're wearing the hat.

Glue second strip of velcro in the middle.

This will prevent the spikes to move too much if the clips get loose.