You think that the backward compatibility is not important? Interesting...
Yes -- in case of OpenXcom -- I think it is absolutely not important.
Btw. there are literally dozens of breaking changes since 1.0.. you would make DEVs spend days if not weeks on functionality nobody (except of you) is using anymore.
Do you know about that: https://en.wikipedia.org/wiki/Backward_compatibility
Quoting from your Wiki article:
Benefits and cost
The associated benefits of backward compatibility are: the appeal to an existing user base through an inexpensive upgrade path; and the network effect, which is particularly important, because it increases the value of goods and services proportionally to the size of the user base. The associated costs of backward compatibility are: a higher bill of materials if hardware is required to support the legacy systems; increased complexity of the product which may lead to longer time to market, technological hindrances, and slowing innovation; and increased expectations from the users in term of compatibility.
The benefits to the user base (i.e. 1 user = you) are clearly much lower than the associated costs
But jokes aside... this is a purely religious topic for you I guess.
There is no way we are going to convince you otherwise.
Just know that if this was "absolutism", the DEVs wouldn't do it as they clearly don't see the need for it.
If this was "democracy", you would be heavily overvoted by the majority who doesn't think it is necessary.
Either way, I see no way how your request can be done...
... other than you create your own fork and do the changes yourself.