Locking cell based on criteria - or removing formula once data h

I have a interesting one, which I need help to crack if it is possible.

I want to be able to lock a cell once speciifc data has been centre, or copy and paste data from one cell to another then deleting formula from original cell.

My formula is a picking a date up from another form only if it is greater than or equal to todays date.

If it meets this, the date is now in the cell... however I need to remove the ability to change the date on this sheet as we need it to measure delays

Formula is in column X and I want to copy information the date to column H then delete the formula only if there is a date in column H

Couple of problems I am have...

So for example

x6 has date of 27/04/2014 (=IF('Scheme input'!$C$33<=Milestones!$C$3,Milestones!I6,"") then copy to H6
remove formula in X6
and then on to the next row.. and so on...

If there is only a formula and no data then I need to leave that in cell and move to the next row.

I manage to write VBA the complete first line, but there is a problem with the next line... and I also realise if the cell remain blank(H) would the VBA us that cell to copy data into as it was the next avaiable empty cell..

Thanks in advance for any advise

Debs