The Official Last Epoch General FAQ discusses this subject and its possibility after launch:
Will there be character customization or gender options added to Last Epoch?
Last Epoch is a class based game and we prioritized creating distinct silhouettes, visual themes, and animations for the different classes over the ability to customize their appearance. There is a lot of work that goes into creating a distinct player character, such as voice acting, modelling, rigging, skinning armor, creating animations, and adding character customization would increase a lot of that work, even doubling it in some cases.
However character customization is a feature that has been very frequently requested, and one that we enjoy from other games. We also have a lot more resources and technical capability than we had when we first scoped out the project, so character customization is not entirely off the table. Those resources are needed in a lot of places though, so regardless of what we decide long term, character customization will not be a feature for the 1.0 release of Last Epoch. As we’re reworking older content of Last Epoch, we’re also keeping this avenue in mind to not make things too focused on the existing pre-set characters to keep things open for this in the future such as cinematics and dialog.
The devs also discuss this topic during an interview performed by Twitch streamer Zizaran. You can watch the full developer response regarding this topic in this YouTube video , which should start at the relevant section (35:15) of the video. If not, timestamps for all subjects discussed are in the comments.