The problem you may have is having the right "parts" to do the job. First off is the oil, and it isn't cheap (around $59.96 where we are at), then you have the washers (3 total, two of one size and one of another) an o-ring (for the one washer) and the filter. If you have those you have got a good start. But the oil is important, when you picked up your Rocket it should have been filled with semi-synthetic oil (5 qts.). You have to drain all your oil out but there are three different drain plugs to undo to properly drain the beast. Then you have to ensure you have the Mobil 4T (again 5 qts) which is a fully synthetic oil, if you use something different you had better make sure that the "service department" at the dealer tells you that it is a suitable substitute ...there are less expensive alternatives for the oil but make sure you have the right stuff. . I'm not sure what kind of checklist you are using to do the 600 mile service, but the dealer has one provided by Triumph that is pretty thorough.
Now I imagine if you have a receipt that shows all the parts, fluids necessary to do the 600 mile service, then your service department will hopefully stamp your book.. They may not like that you did it yourself (after all they are going to make some money on the labor to do the service but it is also how they stay in business to be there for you if you have a problem...note: not all dealers have subscribed to this behaviour) , but again the receipt for those parts is the key. If you bought them from your dealer then you shouldn't have any problems.
Dennis