É possível atualizar o mecânico do UA Artificer (página 4 do documento vinculado ) A descrição do servo não menciona essa possibilidade em sua descrição. Para fins de conveniência, a passagem de texto relevante é apresentada aqui:

At 6th level, your research and mastery of your craft allow you to produce a mechanical servant. The servant is a construct that obeys your commands without hesitation and functions in combat to protect you. Though magic fuels its creation, the servant is not magical itself. You are assumed to have been working on the servant for quite some time, finally finishing it during a short or long rest after you reach 6th level.

Select a Large beast with a challenge rating of 2 or less. The servant uses that beast's game statistics, but it can look however you like, as long as its form is appropriate for its statistics. It has the following modifications:

• It is a construct instead of a beast.
  
• It can't be charmed.
  
• It is immune to poison damage and the poisoned condition.
  
• It gains darkvision with a range of 60 feet if it doesn't have it already.
  
• It understands the languages you can speak when you create it, butit can't speak.
  
• If you are the target of a melee attack and the servant is within 5 feet of the attacker, you can use your reaction to command the
  servant to respond, using its reaction to make a melee attack against the attacker.
  

The servant obeys your orders to the best of its ability. In combat, it rolls its own initiative and acts on its own.

If the servant is killed, it can be returned to life via normal means, such as with the revivify spell. In addition, over the course of a long rest, you can repair a slain servant if you have access to its body. It returns to life with 1 hit point at the end of the rest. If the servant is beyond recovery, you can build a new one with one week of work (eight hours each day) and 1,000 gp of raw materials.

Como você pode ver, em nenhum lugar afirma que você pode ou não pode atualizá-lo para melhorar as estatísticas que você escolheu pela primeira vez. Eu pessoalmente acho que cabe à digressão do GM permitir ou não.