Regarding the Minhagei Yom which can’t be done on Shabbos, such as writing a pan etc they should be done Friday anytime, no difference of before or after chatzos. (The Rebbe 10 Shvat 5717/1957 )
Kovetz Gimmel Tammuz Hebrew Version (70 pages):
Kovetz Gimmel Tammuz Heb/Eng Version (92 pages / includes letters in English and Mishnayos with English Translation)
Many more Gimmel Tammuz resources can be found here
A Special Feature Magazine from Hamodia about the Rebbe (Heb) here