Very good question. Glad you asked.
Just for context, in the US, many music curriculums have ‘elective’ classes that can be taken in addition to the music major. So its a fair analysis to understand that this is the exception to a curriculum and not the norm.
I did the same thing, and I’m glad I did. I studied the music in college, then learned the technology after. Classical training gives you and edge and competitive advantage which for me, many times was the difference between being able to stay in music vs get a day job. So you’re doing a good thing.
As far as how to train, sound engineering can be learned outside of the university, musicianship can not. You will never be able to immerse yourself in an environment where you can grow and be challenged by the most elite musicians in your country without attending a university.
Also, the credentials and the degree in sound engineering don’t carry as much weight in the modern market as the training you can only receive from a university as a musician.
I learned sound engineering simply by doing it. Start with a small rig and record anyone you can, even if its for free at first. Edit these projects. Mix these projects. Download example projects and study them. When you need tips and advice on where to place mics, and how to use tools such as EQ, compression, time based effects, and DAW techniques, I watched tons of videos online. Anything you can find that makes sense. Also, post stuff on ‘bash this recording’.
Try different compressors and EQ units. Isolate an acoustic guitar track. Apply different kinds of compression. Play with transient designer plugins, saturation plugins, and doubler effects. Get familiar with what each type of processor does to each source. Learn basics of where to place microphones through experimentation. There are hundreds of different mics you can place on an acoustic piano. There are dozens of different ways you can position them. There are some basic laws of physics that will help you understand why something DOESN’T work, but they’re not mandatory to know. Your ears will guide you much more than mathematics will.
Also, read articles on the internet, and spend time reading magazine articles. I assure you that a self-taught engineer can eventually learn to compete with other pro engineers. Find someone to apprentice or intern with.
If you have survived a classical music program at an accredited and respected college, you most likely have the musical instincts to compete in this field. Having both piano skills and practical experience with sound engineering will go a LONG way if you’re looking to do this for a living.