One of your premises, "the situations described remain the same exactly", is incorrect.
The situations described by your first set of sentences are not quite the same as those described by your second set of sentences. For example, "I am wearing" is not the same as "I have worn"; the first says that you're currently wearing something, and the latter implies that you are no longer wearing it.
If you want to change the position of that phrase without altering the meaning, there are other ways, like, for example, instead of:
Today, I AM WEARING ice skates for the first time ever.
you could say
Today, for the first time ever, I am wearing ice skates
or, somewhat awkwardly, in my opinion:
I am wearing ice skates, today, for the first time ever.
I think it would help you to get rid of the extra words, when thinking about this.
I am wearing
I wore
I will wear
I have worn
I had worn
I will have worn
This way you don't confuse yourself as to whether the subject of the verb is "Today" or "I".
For example, in the sentence "Today is the first time I have ever worn ice skates.", the subject of the "is" is "today" (hence the present tense), whereas the subject of the verb "wear" in the second sentence is "I", and you are already wearing the skates, so you "have worn" them (even if they are still on; the act of wearing occurs when you put the skates on your feet).
