(You could create a hidden coda, adjust the gap as desired then put a rehearsal mark and drag it to the gap position in Engrave mode, then readjust the bar numbers as needed.)
Or just create a staff attached text with border and erase background (adjusting the padding as desired), to hide the lines of bar 18, and set the opacity of the bar rest in bar 18 to 0% to hide it. You can then set the opacity for the real rehearsal mark to 0% to hide it. And adjust the bar 18 width with a local note spacing change, and a reset one in bar 19. And also here you may want to adjust the bar numbering from the current bar 19, to mach the “repetition”.
Do you know if I can copy the changes made in this menu and paste them in another symbol? I want to do it to change the position of the rehearsal mark included in the particella:
Yes, you can select the boxed text in engrave mode, then from menu Edit choose Propagate Properties.
You can also copy and paste the Note Spacing changes in Write mode, from score to part: select the first NSC, use the select more shortcut or from menu Edit > Select more, copy then select in the part the barline and paste them.
To not have the multibar rest 1 on bar 18, you can add there a Chord Symbol region (that will break the multibar rest), and then you can hide the remaining bar rest as explained.