Sure it’s possible. I did a few (in assets.csv) like
#,sim_book,Yogabook,Yoga,books,Discover your inner world through bizarre body positions,book_om.bmp,71,100,28.50,0,“REBUYABLE”,609,showdetails,#,#,“yoga,0.1,1.0”,“stress,-0.23,0.91”,#,
#,boardgame,Board Game,general,Play until everybody quarrels with everyone,ass_citadels.bmp,87,128,34,0,“STEALABLE,SELLABLE,REBUYABLE”,#,#,
You just have to create a bitmap and corresponding activities (as with yoga above).
For walking a dog, I suggest somethig like new activity (in solo_activities.csv):
#,dogwalk,Dog walk,Allow the dog to lead you in muddy places,play doghowl.ogg,0,default,0,0,0,-1,-1,1,1,1,1,1,1,1,#,“boredom,-0.2,0.25”,“stress,-0.04,_STRESS_DEGRADE”,“fitness,0.09,0.85”,“weight,-0.01,0.92”,“tiredness,0.20,_TIRED_DEGRADE”,#,“dog,1.0”,“dogleash,1.0”,"_energy,0.2"
Cheers, KudosPhoebe