Design Engineer as an SDK/service

I am considering offering my services as a software designer and engineer to other established companies in bite sized discreet small tasks. What I mean is that instead of hiring me as a full time employee, a PM or a department of a company could hire me to work on one specific feature. It could be just to work on the design of their buttons, or it could be like the login flow or just their Modals, etc. Basically they could hire me to improve any part of their product big or small. I would submit the completed work in the form of a PR to their team. The huge main issue is security and permissions to their company and codebase for small work like this. A company would not want to put in the effort to get one person all set up in their env and roles etc for just like 1 month of work. So what I am thinking about doing is building an SDK their team would install that could manage their dependencies and gives me access to to the modules required for the work. It would create a sandbox env for me to work on whatever part of the product they want. So it would be like hiring an agency for a chunk of work by using CLI to set up the sandbox env for the agency to do the work and submit the completed PR into their env. Is this dumb?