1) You wrote:

“I've tried using a expression and the midi tool but it doesn't work.”

Please specify the exact steps, so that we can reproduce them.

Also, we need to know the time signature (- 4/4? - 3/4? - 2/4? - 4/8? - or?)

2) To “erase a single note in a measure without moving the other notes”, in the Simple Entry Tool select the note, and hit the letter R key.

Sorry for my bad english, it's not my native language.

So, I tried different things but it doesn't seems to work. can you tell me te best / easiest way to make the playback "swing the 16th's notes" in 3/4 and in 4/4 ? (My piece combine different time signatures and feel.) How would you do it if it changes many times in the same piece ?

And what i was saying about the simple entry tool is that, for exemple : (maybe it's obvious and it's my bad) 

But, If i have a measure in 4/4, with 4 quarter notes and I want to change the third one and remplace it with to eight notes,

How do I erase the third quarter note without changing the other note/s (which would be the last quarter note) in order to enter the two eight notes that i want ? 

Do i have to set something in document options or anything else ?

It's maybe pretty simple but when i have many subdivisons it's really long to always erase the whole measure.

Thanks for your reply !

1) What would be the best / easiest way, depends on the actual, musical context.

One way to do it:

An expression with playback effect Swing always bases the Swing on the time signature’s beat duration (= the “denominator”).

For 3/4:

Set the “real” time signature to 6 eighths (= 6 beats with a duration of an eighth), and set the “display” signature to 3/4.

For 4/4:

Set the “real” time signature to 8/8 (= 8 beats with a duration of an eighth), and set the “display” signature to 4/4.

Since the “real” beat duration is an eighth, an expression with Swing effect will create Swing 16ths.

2) With the Simple Entry Tool you can enter the eighth notes via clicking.

If you - with the Eighth Note Tool selected - click a quarter, then that quarter will turn into an eighth.

Thanks It works !