No, adding to the target list will not trigger any emails being sent; only the actual event of sending the Campaign will send emails (using the version of the Target list as it was at the moment of sending).
is there any solution that you propose to use so as to keep the flexibility of inviting customers?
I understand that if i manually choose to send email via campagin it will send emails to all contact on target list, so some email users may recive it twice.
I am not a Campaigns expert, but I believe Campaigns are ready to be re-used with the Marketing email name concept, described in the Docs like this:
Enter a name for this run of the campaign. This allows you to resend the campaign at a later date to a different target list, or with a modified template. The campaign will store separate status details for each marketing record, and these can be selected on the campaign status page.