Whether you learn from a person in a group class or on your own from a video on the internet or a dvd; part of becoming skilful is being able to see and copy what is being shown on first a gross and then an increasingly subtle level. This is far from easy and is made even harder for those going the self-instruction route as they won't get much or any feedback on their efforts to copy what they see. [Should I really say "What they think they see!"].
I suppose that a really experienced practitioner can also cross over into unrelated arts and use, for example, experience in Tae Kwon Do solo forms to try and teach themselves Xingyiquan solo forms; but it will be even trickier to understand the differences as well as the superficial similarities between how the new system being studied "powers" a solo form based on very different principles from what you may have been used to. Accumulating solo forms from a variety of unrelated styles can be useful for a period of time; but serious practitioners usually end up focusing on a more limited number. The better practitioners do, in any case.
Keeping these caveats in mind, I do think that it's a great idea for experienced practitioners of any style of Taijiquan to try and teach themselves "variations on the theme" as it keeps the brain active [particularly for older practitioners] and can lead you to new understandings as well as possible new directions in your training. It is also important to remember that no one form of exercise can provide all the needs of your body. I was told in my early years of instruction in the Yang-style [1970s] to avoid all other forms of exercise or hard-style martial arts aside from the Yang-style long form that I was learning as it was "a perfect exercise". Now I know that's nonsense; but there are still people teaching that way. Despite what some may say or imply, you need to vary how you exercise for the state of your health and fitness and if solo forms are what really turn you on -- at least learn a variety of such and vary your training regularly.
When choosing a solo form to work on, look for as many variations of that same choreography as you can find, study them all and pick what seems to you like the best example. Don't be fooled by forms that are very gymnastic or feature very low stances as complexity and difficulty are fine -- if you are up to it physically -- but not always a true indication of the value of a particular choreography. Conversely, what seems like a simple solo form isn't always as easy as a good practitioner can make it seem on video.
Follow only one particular interpretation while learning a rough draft of the entire solo form you have chosen; practise that for three months [m inimum] and then study alternative video versions of the same form and change your performance as seems suitable to you from that comparison process. I might add that you can sometimes learn something of value by watching terrible versions of solo form work in that you can reinforce your commitment to quality in your own work! By the way, it can be a great idea to do periodic video records of your own efforts and review those to improve the weak areas in your execution.
It is arrogant to assume that your self-instruction efforts will automatically produce the same results as quality hands-on instruction; but that doesn't mean that there isn't value in making the effort. Personal long-term instruction is always best, because of the feedback from a good instructor; but this doesn't mean that you can't benefit from self-instruction if you are determined; even if you only practise a particular solo form for a period of time before replacing it with something else. The learning process is what is important and not locking yourself into another stylistic "straight-jacket".
Copyright Michael A. Babin ©2018