Tractate Shabbat Magg 1

Shalom Rabbi in Tractate Shabbat, page 34, page 1 – in the Tosafot speech beginning with ‘A’dan A’liyo’
It seems that Rabbi Shimon’s method can be understood in two ways:
On the one hand, it can be understood from the Tosafot that Rabbi Shimon does not believe at all that the oil from the candle is to be used for a whole day, and for you, he permits the oil from the candle to be used for a period of time.
On the other hand, it is understandable that Rabbi Shimon’s opinion is that he does believe that a demigo is a deed, but he reserves the rule for cases in which there was no intention to use the object after it had completed its function.
Is there a way to determine Rabbi Shimon’s opinion on this matter?
And a second question –
When Rabbi Yitzchak excuses all the “I am the one” in “Deshani Haka D’Tshiriki Lemko” (The place where the “I am” is needed)
It seems strange to me that the permission he gives to the prohibition is the prohibition itself.
In other words, if the prohibition is to use a tool for something that is not permissible, this permit does not deal with the problem at all.
After all, every time I pick up some tool with permission, I can use it to do the very thing we came to prohibit.
I would be happy to explain this issue as well.
thanks