There are concerns with diluting, re-aerating and/ or re-pitching:
-Stressing the yeasts can lead to off flavors or poorly developed lipid layers in the cell wall (reducing alcohol tolerance and promoting premature cell lysis).
-When diluting the must, sugar is not the only nutrient to consider. Nitrogen sources, vitamins and other growth factors can become limiting…Especially if you have already gone through a partial or full primary fermentation. Again, this will lead to stress.
-It takes a period of time for cell mechanisms to adjust to changes in culture conditions. Switching back to aerobic conditions after the yeast have geared up for the anaerobic fermentation cycle can waste a lot of cell energy and nutrients (in addition to causing stress and off flavors).
In general, it is good idea to give your bugs all that they need (nutrients and growth conditions) and allow them to go through a nice, natural fermentation process with little or no interruption. Under these conditions, you can be assured that your yeast will perform as advertised in terms of alcohol tolerance and flavor characteristics. However, if you don’t have a “perfect” fermentation it does not mean all is lost. Depending on your recipe, you may have components that will mask off flavors (fruits, spices, beef jerky, etc.). Also, you may generate off flavors that you find appealing (i.e. some people like a lot esters, others do not). As Oskaar mentioned above, post your recipe and original readings…There are many experienced brewers here that can offer good advice.
Personally, if I had a mead that was too sweet I would combine it with an overly dry batch to balance out the flavor before I would try to dilute/ re-pitch.
Peace.