After a healthy evaluation, Foldit team allowed me to share this recipe.
Use: the recipe is self explaining.

I use it mainly to keep my bands in design puzzles: I make a copy of my bands between sheets and I keep them in a note (usually note 18). Later on, I can recover my bands by importing them.
Other use: hand writing of bands (of copying from a worksheet) and importing them.

Note: check that the format of export and import are the same (e.g. including sidechains or not).

The option "side chain" has no big use unless for keeping bands between cysteine (keeping disulfide bonds). Too many bands are not well handled by fold it (very slow for computer).

Note that the option "side chain" is always extremely long (even for copying one unique band) because the recipe has to scan the all protein in order to find the bands.

Format to import can be seen when copying a band to export. It depends whether you included sidechains or not.

Default format (without sidechains) for importing your own bands (for 2 bands):
segfrom-segto-length-strength-enabled
Delimitor between successive bands is space " "
Delimitor of fields is "-"
All fields are mandatory

Example for 2 bands:

89-11-14.695068745868-1-1 87-13-16.514458556754-1-1

With sidechains, example for 2 bands:

89-11-0-0-14.695068745868-1-1 87-13-0-0-16.514458556754-1-1

Atoms numbers are in positions 3 and 4, all other fields are the same as above.