I have not fully understood your question but I will answer it to closest I can.
Salawat is the plural form of the word Salat which simply means ‘to call' as in prayer.
Salawat is mentioned in the holy Quran in surat al-ahzaab 33 verse 55 :
Indeed, Allah confers blessing upon the Prophet, and His angels [ask
Him to do so]. O you who have believed, ask [ Allah to confer]
blessing upon him and ask [ Allah to grant him] peace. Quran
This is mandatory on all Muslims and will be deemed utterly disrespectful (to unimaginable extent) that a Muslim will skip this salutation on the prophet.
It is mandatory on the person who calls the prophet's name either alone or in speech, he must say the salutation. Usually the salutation is "Peace be upon him" in English or "allahumma salli 'ala muhammadin wa ali muhammadin" in Arabic. The Arabic version is more correct and has the meaning of "Oh Almighty, send peace to Muhammad and all his family". So, for the question, if the speaker repeats the prophet's name 50 times, he has to perform salutation 50 times. A short version might be acceptable but not recommended.
Anyone who listen the prophet's name (even if he does not utter it) must also perform this salutation. Although in this case their is leniency. If the speaker repeats the prophet name too often, it is acceptable for the listen to just say it one time (the first time he hear it), but can repeat it with every mention of the prophet's name.
When you write and the prophet's name comes in, it is natural to perform this salutation. There is no skipping because the salutation is not for show off, it is out of utmost respect, which every Muslim has for his beloved prophet. Also it is more convenient to say it when writing because writing cannot be that fast.
For a non-Muslim
I do not think it is compulsory for a non-Muslim to perform salawat. There is no compulsion in Islam. Islam never dictated anything on non-Muslim. Because non-Muslim would be allowed to drink in a Muslim country even though it is haraam for all Muslims.
Also there is reward for performing salawat for Muslims. Every time they say it, Almighty God gets happy with them and gives them reward.
Just a little note
While it is compulsory to perform salawat for the prophets, many scholars especially in west believe, the same should be done for God himself and they believe that is even more important because God is the supreme being. The proper way to salute God (Allah) is Subhana wa t'ala (Glorified and Exalted is He).