Hi Joao,
This is a feature that has been available in CHIRP for nearly 5 years. Here is how you use it.
1 click on a memory row to highlight it
2 press ctrl-a to highlight all of the memory rows
Note: you can use any combination of click, shift-click and crtl-click to select the memory rows that you want to edit
3 click on the [Properties] button at the top of the spreadsheet style memory editor (an alternate method would be to right-click on a highlighted memory row and choose "Properties" in the menu that appears)
In the Memory Properties menu that appears you can now...
4 tick the box to the left of Power (and any other setting you wish to change on all of the selected memory rows)
5 select the desired power level (and select any other setting that you enabled in the previous step)
Note: don't forget the "Other" tab can be clicked to access "extra" per-channel settings
6 press the [OK] button to confirm the changes
The power setting for all programmed memories has just been changed.
Jim KC9HI