I know this seems like a good idea, and congratz on having job security and a good job but think a bit about how this will affect your daily life.
If i had a friend change their name to "yggdrassil" (yeah i love tales but i cant fucking spell that shit and nor can anyone else) id refuse to call them it. Ever. Theyd still be their original name. Theres changing your name and taking the piss and i cant say id bother changing my habits whatsoever.
1. You would have to spell your lengthy name out EVERY DAMN TIME to even remotely get them to spell it.
2. A LOT of people will accuse you of taking the piss and not believe your name is that. People dont react kindly to
feeling they are being lied to.
3. I wouldnt use the new name. I wonder if your friends would?
4. Things like taking a delivery and signing off at work become hard and rediculous, i triple sign about 5 documents a day that my manager will directly review, and MANY beside that. I know it seems fun now but id become a little pissed i i had to continuously read "yggdrallis" over and over and over and over printed on my companies documents.
5. Giving out your name casually in a public space WILL be awkward. I know it seems fun to tell one close friend with a planned introduction but being suddenly thrust into a group and having to say "Im mithos yggdrassil" will make a seriously bad first impression, or an awkward one. This isnt your fault. Its just gonna be super awkward. See point 2.
6. I hate a lot of the things i liked 4 years ago. I got sick of them. I suddenly realised they were good but not THAT great. I moved on and changed. Course you can change it back in 3 months. But hearing a reference over and over again makes it stale and you start to hate it. The cake is a lie? Hahahahahaha... in 3 months you might decide perhaps the name is intensely annoying.
That said Siefer isnt a bad name. Id avoid anything with titles. No one is going to use a title because it sounds like a grab for respect. And people are very likely to disrespect someone who attempts to garner respect by forcing an honorific title. Even if thats nor your intention. Go for Siefer.