Hi Sonshine,
Even though Shewolf13 has posted while I was typing, I'm going to still post my answer as well.
In general, 1, 2, 4, 5 and 7 can either return your sim to the start of the current life stage or take some days off your life (I don't know for sure which is which). This gives you extra days to achieve your requirements which isn't permitted. Specifically on the individual items.
1 You can have a tattoo on your sim at the start of the game though, give them one while in create a sim.
2 Basically if you put your sim in the Stylist career, give sims who you are not likely to want to use in your dynasty the makeovers (so avoid giving them to sims who you may want to put in your household or who you are wanting to be best friends for your targeted immortals.
5 The Steam-It-Up Sauna is a piece of premium content that you can give mud baths with. This is a different item to the Volcanic Clay Bath and the Mud Facial in the Spa Rabbithole around town. You can use all the options available from the Spa Rabbithole, however.
7 Cows from the milking station premium content can give different kinds of milk depending on what you feed them. Normal milk, chocolate milk and soy milk are the types I know. Soy milk adds extra days of life to sim by reducing their age, so that's why you are unable to give it to non-immortal sims.
8 It was recently discovered that if you are carrying unknown special seeds in the personal inventory of a sim and they die either of old age or one of the other death types that if any of those unknown special seeds are a death flower seed that Grim will take the seed away and permit your sim to continue living. So, if you do collect unknown special seeds, after your sim picks them up, you can drag them from your sim's inventory and put them on your home lot. If you can get something that stores items (bug collectors cabinet or either of the two elixir cabinets are my favourites for this) you can drag them directly to the storage cabinet to store them securely. Alternatively, if you have a basement or flat roof that no one can get to, you can put the special seeds in either of those places.
Hope my explanation helps and please ask if you have any further questions, Sonshine.