How to customize the appearance of OSM maps on Garmin GPS device?

Just downloaded my first OSM map onto my Garmin etrex 30x from http://garmin.openstreetmap.nl/.
I always liked the extremly fine level of detail of OSM, as compared to other maps I know it contains really about every dirt path there is.

The map I just downloaded is working fine, however there are a few details I’d like to change.

• There are way to many points of interest (grocery shops, gas stations, hairdressers etc.) marked on the map and I almost can’t read anything. I’d like to delete these points category-wise (say, remove hairdressers but keep gas stations) to only keep what’s relevant to me.

• I’d like to change colors and line types of streets (say, make all trails a fine black dotted line and all highways thick and purple).

• I’d like to adjust which elements show at which zoom level (say, only show trails when the area shown on screen is smaller than 20×20 meter).

Is there any software (preferably free) I can use to make these changes? Is there any website where I can customize these things before downloading? Or is there any other source of finely detailed maps I can use (relevant region is Central Europe)?