We are a very small software company completely focused on the maintenance of its software product, we do not accept changes to the architecture nor the design of the product.
Question1: Can we interpret TS SP 1.1 “Develop alternative solutions and selection criteria” as the different ways that the development team gives to the customer to solve the customer requirement through already implemented options of the product?
The development team says that there is no room for evaluate alternatives for design, because there are no changes to the design of the product. If a “new” customer requirement needs a change in the design of the software product the requirement is rejected. In this case and only if it is possible, the development team gives different alternatives to obtain or process the information using already implemented options.
Question 2: In this context, Can we interpret TS SP 1.1 as the alternatives of coding the specification? There are always different ways for coding the same specification …
Great question! Remember that SP1.1 “Develop alternative solutions and selection criteria” is about both creating a set of criteria and generating a list of potential solutions. So the first part, the criteria, should be no problem for you. The criteria you set may very well lead you down a path of NOT generating alternatives, or it may guide you to select different approaches to solving the problem.
There is no requirement in this practice that you evaluate different architecures or designs. It only speaks of "solutions" which could be code snippets you re-use, different coding techniques, a library that you purchase and install, or the various combinations of options that you refer to in your question (these are just some examples).
You can also view SP1.1 as "alternatives to coding" as you mentioned. The spirit of the practice is that you have explored different options to solving the problem using pre-determined criteria.
If this sounds like DAR you're on the right track. It's essentially a DAR process customized for solution design and implementation.