Hypothetical 1:
Let's take your example: An AFC team is willing to pay Tavon 6 mil per year in 2018 and 8 mil per year in 2019 and 2020. (As opposed to the Rams current deal of 8 mil for 2018, ans 9 mil per year in 2019, 2020, and 2021)
In this scenario, the Rams would convert $6M of TA's salary base into a pro-rated bonus as follows: $2M in 2018, $1.3M in 2019, $1.5M in 2020, $1.2M in 2021. Upon a trade, the Rams would immediately have that $6M go onto their 2018 salary cap as dead money. The other team would be paying TA $6M less on the restructured contract with the annual amounts being what you propose.
The problem with this scenario is obvious, the Rams wouldn't be willing to absorb $6M to not have Tavon play for them when they are only on the hook for $5M guaranteed next year. Currently, they can cut him after the season and only owe him $5M. Also, the Rams can't make the 2018 dead money hit more palatable. Basically, whatever pro-rated amounts are remaining on the contract will go onto their 2018 books as dead money. In this scenario, that amount is $6M.
Whether Tavon would do it or not comes down to what does his agent see as his value on the open market. Is he worth more than a Kenny Britt ($8M) or Mohamed Sanu ($6.5M)? Darren Sproles ($4.5M)? Or something in between? If he thinks he can get $7M plus on the open market as a multi-purpose weapon he probably doesn't cooperate with any plan to lower his salary.
Hypothetical 2:
My example: Find a team willing to take a chance on him in the $5M range for 2018 with the remaining contract in tact.
In this scenario, the Rams would convert $3M of salary and roster bonus into pro-rated bonus money over the remaining 4 years. Upon a trade, the Rams would immediately have that $3M go onto their 2018 salary cap as dead money but it would also save them $5M. IMO, a $5M savings is quite a bit more attractive than a mere $3M savings.
The other team would be taking a chance that TA would be productive for them at a palatable number in 2018. If he produces akin to what he did in 2015, the remaining years on the contract are actually reasonable. If he doesn't produce, they don't owe anymore guaranteed money and can move on. They could cut him outright after the 2018 season or ask him to restructure a pay cut and at that point have the leverage since he would have had several subpar years in a row.
There may be other hypotheticals that work but hopefully you can see from these two how restructures work.
