これを試して:
Dim FullText As String, l() As String
'''Open file for reading using Scripting Runtime. But you can use your methods
Dim FSO As Object, TS As Object
Set FSO = createbject("Scripting.FileSystemObject")
Set TS = createbject("Scripting.TextStream")
Set TS = FSO.OpenTextFile(FilePath)
TS.ReadLine 'Skip your first line. It isn't needed now.
'''Reading the contents to FullText and splitting to the array.
FullText = TS.ReadAll
l = Split(FullText, vbNewLine) '''the main trick
分割すると、l() のサイズが自動的に変更され、すべてのデータが格納されます。
これで、l() 配列に必要なものがすべて含まれるようになりました。