Can we say "a sentence would instead end with something", or is it safer to put it at the end of a sentence? Thanks :p?

Both are correct. The first is usually used aloud.

This is more a question of style and intent than of grammar. You may say it either way. instead end is how I would say it, because I mean to propose that the following phrase is the alternative condition, rather than stating that your action is the alternative, which is the main idea that would come from placing instead at the end.

that is, instead end means that you will present an alternative way to end.

end with something instead gives a more general idea that you could do other than end (for example, rather than keep talking about the details of your point, you could end with a summary statement instead).