It's not really a spore, more a super resistant bot being a bit lazy!
Easy enough to do though, take a working bot and decide on your conditions to become a 'spore', something simple like (*.eye5 0 =) will do to show how it would work.
All the genes in your working bot now need the extra condition (*.eye5 0 !=) so that they become inactive when your 'spore' conditions are met and only work when the condition is not met.
You then have a bot that will do nothing when its 'spore' condition is met and can add another gene to tell the bot what to do when it is a spore. (100 .mkshell maybe but this costs energy!)
A more complicated version with multiple spore conditions or a whole set of conditions to meet before it switches the bot back on can be done by using a memory location but I'm guessing you aren't worried about that yet.
The last bot I posted, Bubbles, uses a similar technique, switching off most of its genes if it is poisoned or paralyzed and activating a suicide gene instead of a 'spore' gene.
BTW (Question for someone:))I take it that shell and slime can be used at the same time? Are there any disadvantages to using them together now?