AI'm learning new piping techniques, but it seems like my icing isn't stiff enough for some of them. I know buttercream or royal is the best, but my homemade cream cheese icing is my signature thing. I've tried adding a little corn starch, which helped some, but I'm afraid to add too much. Also, I'm curious if baking paraffin is an option?

as a pro not icing cakes just straight decorating i always had a squirt bottle of water to thin my icing and cornstarch to thicken it as needed throughout the 8 to 15 hour shifts --

paraffin might be an option although i've never added wax to my icing -- you would have to melt it into the fat to get it to work -- which i think would blow your icing idk -- cornstarch works great -- keeping in mind sometimes it's better to make an icing especially for piping -- other than that why not use enough cornstarch?

For a cake covered with Cream Cheese icing (carrot, pumpkin, banana) I also find that the Cream Cheese icing is very soft and difficult to pipe.  I rarely do anything other than simple borders and I had to add a bit of powdered sugar to stiffen the icing before even piping those (same as @-K8memphis  used corn starch.)  I just consider it a "desert cake" and don't decorate it up much.

CC icing in and of itself is a softer icing, but a few things can aid in it's pipability.

You can up the amount of butter you use in the recipe (generally no more than 50% butter and 50% cream cheese or you wont taste the cream cheese) and that will help it behave a touch more like a buttercream, and if you are just going to pipe borders and what not, just dose your icing with more conf. sugar to get it nice and stiff.

My CC icing is fairly standard 12 oz CC, 4 oz butter, 2lb conf. sugar, some salt, and a touch of sour cream.  I would never dream of using it as it is to pipe anything other than a cupcake swirl.  I would modify it in the above ways for anything more.

And anyway, I never ever frost a cake in CC, I only really use it as a filling (as CC icing breaks down fondant) so I have never really had the need to modify.