How to insert text in specific blank lines?

Hi,

May someone help me in how to add the word "SUB_BLOCK" inside the "BLOCKS_TYPE_1" that have empty lines between text, and remove rest of empty lines.

The Column1 looks like this

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("hZLLDsIgEEV/ZcLaha3vhYsWatOC0kgrVtL0//9CxFhfGWYWkwAnd3Lv4BzLleZybPumGBM2zBwLDZDKYA9JlMg9sYoS3BMLepTw2DxKFBNBCi1JobirciLQ9hckppVN/jHikWFKZrglXa9J17socfjeFG44/XnCBF/mNiTFyZX4OgIZpa8zvL/kR+8uHDKpQFZGV1C2xppwf+1vT+CkVdNYkKIW4SythdoI4B5nw3AH", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [COLUMN1 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"COLUMN1", type text}})
in
    #"Changed Type"

COLUMN1
BLOCK_TYPE_1

                        A = 1
                        B = 5
                        C = 3

                        D = 0
                        E = 0

                        D = 4
                        E = 1
                        G = 1





BLOCK_TYPE_1
                        A = 3
                        B = 2
                        C = 8
                        D = 6
                        E = 9
                        F = 3




BLOCK_TYPE_2


                            B = 7
                            C = 1
                           M  = 3
                           R  = 5
 
 
UVC AKL KISOI GTSWS
XYZ 
NOLPPW KDJD
KWW JSD COI 

Below is the input column and output column I'm looking for, to the right, showing in yellow the "main block" lines and the new "sub blocks" lines in blue and rest of empty lines removed.