Money maker and rare romance
If you have a jeli this is a really good cheat. Go into options and click copy file. The one you are copying should be the one you want. Go into the copy, then Gretchem Fetchem. Choose the post box and put the rare in. Send to old file. Romance and sell the baby: soon you'll be master romancer.
Alternate Title Screen
Get 100% completion in your file to get an alternate title screen.
The Cake is not a lie
When your Birthday comes up in the DS's Internal Clock, you will get a Birthday Cake. The Birthday cake has Romance and Happy Sweets in it, and you will get a Dog Egg or a Cat Egg as well.