您可能会从阅读How to avoid using Select in Excel VBA中受益。
粘贴前请先复制，否则中间的代码会相互干扰。请使用“变量”，而不要选择和激活工作表或区域。使用With块和/或变量可避免代码和工作表名称重复。

Option Explicit

Private Sub UpdateForm1_Click()
    Const ThisWbPassword As String = "1234" ' define password only once as constant.
    
    Dim Up_Location As String
    Up_Location = "T:\Repeats\"
    
    Dim Up_Name As String
    Up_Name = "PNL_UPDATE.xlsx"
    
    Dim WbUp As Workbook  ' set opened workbook to a variable for easy later use
    Set WbUp = Workbooks.Open(Up_Location & Up_Name)

    With ThisWorkbook.Worksheets("CustQuote")
        .Unprotect Password:=ThisWbPassword
        WbUp.Worksheets("Sheet1").Range("Text_1").Copy  ' always copy right before pasting to avoid interference of code between.
        
        With .Range("A35:A39")
            .PasteSpecial xlPasteAll
            .HorizontalAlignment = xlCenterAcrossSelection
            .VerticalAlignment = xlCenter
            .ReadingOrder = xlContext
        End With

       .Protect Password:=ThisWbPassword
    End With
    
    Application.CutCopyMode = False
    WbUp.Close SaveChanges:=False
End Sub

第二次运行代码时，代码会在.Unprotect之后停止运行，工作表处于未保护状态，因此第二次运行是在未保护的工作表上。
通常您会希望使用错误处理来覆盖它，这样您的工作表就不会以未受保护的状态结束。
这是一种基本的错误处理，用于确保在发生错误时再次保护工作表

Private Sub UpdateForm1_Click()
    Const ThisWbPassword As String = "1234" ' define password only once as constant.
    
    Dim Up_Location As String
    Up_Location = "T:\Repeats\"
    
    Dim Up_Name As String
    Up_Name = "PNL_UPDATE.xlsx"
    
    Dim WbUp As Workbook  ' set opened workbook to a variable for easy later use
    Set WbUp = Workbooks.Open(Up_Location & Up_Name)

    With ThisWorkbook.Worksheets("CustQuote")
        .Unprotect Password:=ThisWbPassword
        On Error GoTo ReProtect ' in case of any error make sure the sheet is protected again
        WbUp.Worksheets("Sheet1").Range("Text_1").Copy  ' always copy right before pasting to avoid interference of code between.
        
        With .Range("A35:A39")
            .PasteSpecial xlPasteAll
            .HorizontalAlignment = xlCenterAcrossSelection
            .VerticalAlignment = xlCenter
            .ReadingOrder = xlContext
        End With
        
ReProtect:
       .Protect Password:=ThisWbPassword
       Err.Raise Err.Number 'throw the error message after protecting the sheet
    End With
    
    Application.CutCopyMode = False
    WbUp.Close SaveChanges:=False
End Sub