Why Do We Switch The Tune In Lecha Dodi

לז"נ הקדושים                                              

הרב הגאון החסיד ר' מרדכי יהודה בן הרב שמואל דונאט ומשפחתו הי"ד

                                        י' חשון                  

R. Zalman Geiger zt"l wrote a Kunteres called דברי קהילות.

In it he recorded the Minhagei Frankfurt for the whole year. 

Even though today we don't follow many of their Minhagim

it is still considered invaluable information for all יוצאי אשכנז

even for Chasidim and those who Daven Nusach Sfard. (Arizal)

Most Minhagei Frankfurt hasn't changed for over a thousand years.

Their Minhagim goes back to the Ba'alei Tosfos and beyond.

As the Ashkenazi Yidden spread out to other countries like Poland, 

Hungary etc., many of the Minhagim were dropped and new ones 

were adopted.

There are Minhagim we follow today which originates from the 

Chachmei Ashkenaz the Ba'alei Tosfos. There are others that were 

introduced later. 

What we call "Kabbalas Shabbos" is only about 450 years old. It

was introduced by the Arizal and his Talmidim. The Minhag 

originated in Eretz Yisroel and made its way to Europe & Africa. 

The Frankfurt Kehilla wasn't keen on adopting new Minhagim. 

Originally they would only allow Kabbalas Shabbos to be said

in the old Bais Haknesess and not in the New (Main) Shul.

The Chazzan didn't wear a Talis and wouldn't stand at the Amud.

It was only said by a few individuals. 

Most people Davened in the New Shul where Ma'ariv 

was followed immediately after Mincha and no 

Kabbalas Shabbos in between.  

As time went on, the Minhag was gradually accepted by 

the masses.

Reb Zalman Geiger writes:

 The Piyut of לכה דודי has 9 stanzas the first 4 starts with the letters שלמה talks about the coming of Mashiach. 

The other 4 stanzas starting with the letters הלוי talks about after the arrival of Mashiach which will be even more exciting therefore a happier Niggun.

This new Niggun started at התעוררי 

(Perhaps another reason for changing to a Lebedig 

Niggun because it fits more to the word התעוררי- to wake up אמבצי)

When the Chazzan got to בואי בשלום he went back to the original 

Niggun he started with.

  

For some reason, our Minhag is for the new Niggun to start 

at לא תבושי and we don't change it back to the original Niggun.