Is there currently a modifier that drops your tightends rating if you switch him to a wide receiver? Been noticing that despite a particular player having all ratings in the 90s except acceleration he's a 79? Is this because he's 30% above the weight average? Explain please! And is there a way to set tightends to be your number one receiver and leave them at tightend. I'm in a team that has 2 great tightends and no receivers

Yes, a weight differential will significantly alter a player's overall rating, however by switching a player to a new position they will gradually adjust their playing weight to match the ideal for their new position over time.

oh so after a few seasons he will grow in terms of future overall?

If his future drops then it's probably the difference in the weights for each attribute (you can modify them under MyTeam->EditPlayerWeights - or at least see why he dropped in his future). If it's is current value that drops, that can be attributed to weight and experience, and if you permanently change his position to WR he will eventually overcome that. If you play him at WR but keep him on your roster as TE he won't grow in his experience as quickly (he does gain some from playing time but you lose out on practice time and training camp)

with all due respect have tested out editing player weights, still seems to be much lower than a wide receiver of similar attributes

This is true.

In the players notes, put in his playing weight and then come back to it in a few weeks, you'll notice the change. Some players adapt quicker than other as well though