Merging Cells Programmatically (I know it's not good but the Boss wants it..)

Good Day All

thanks for your help last time, this is a bit of a quick ask but i need to Merge the following Cells Programmatically:

Row 5
Range($N$5 - Columns.Count)
'Columns.Count would be based on Row 7 (the date) Formula

Formula:

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Rows 6, 7 & 8 are hidden helper columns (only done this way, incase i leave the Co. and the spreadsheet breaks, someone else can fix it)

Gantt Chart Pic 1.jpg

We'd like Row 5 to Merge Column Cells if the Month is the same (in this image example Jan & Feb (and on to March as per the Project End Date)) see following image

Gantt Chart Pic 2.jpg


I do appreciate we're not using Excel in it's best guise, I'm Primavera P6 trained, however my co-workers are not, this is a quick fix to create Sub-Plans for a much larger project.

Any help as always will be gratefully recieved.

Link to File Gantt Chart
note: Includes VB from my original post Unable to fire private sub worksheet_selectionchange on user input
And this amazing Pop-up Calendar for Excel