Yup - You can sure use bespoke extensions with the freebie Qlik Sense Desktop, both visualization & mashup extensions.
If you do not already have web dev skills then there is a significant learning curve to writing Qlik Sense extensions, but one well worth embarking on, so maybe worthwhile concentrating on your strengths not your weaknesses.
You could think about downloading some extensions off Qlik Branch, but don't try and pretend you wrote them, just simply tell the truth that you downloaded them from Branch / GitHub.. Most likely any decent potential employer would notice they were from Branch and if they didn't one would have to question whether one would be wise to work for them.
