Is 1.35v RAM labeled as regular DDR3 still considered DDR3L?

Yes it is. Of that I am sure.

Which motherboard do you have? Don't know? https://www.piriform.com/speccy/download can tell you. You can download, install and run that. The summary page https://postimg.cc/image/4lwdzu29f/ will show you your hardware installed. You can see your motherboard's info on that page. You can click on motherboard to see detailed information. You can Google your motherboard's make and model. Go to the manufacturer's website for that board. You can then click on support. You can then click on CPU and memory. They usually include that page. They are CPU and memory QVL lists. Qualified Vendor Lists are not complete. They only show which CPUs and memory modules they have tested with that motherboard. Other CPUs and memory modules may work.

Not likely. Sounds like it's specific for a reason.

i would not risk it unless you can afford to. technically it should work, but then if it is packaged poorly, maybe that company should not be trusted with integral parts...