It is possible that the court will modify the order but there is no guarantee. If you obtain joint physical custody it is worth filing the petition.
This answer is only for informational purposes and is not meant as legal advice.
Agree with Attorney Schwartz, but it's hit or miss on both the joint physical custody and the support issues. Joint physical custody is not the norm, and only works when the parents still live close nearby (like in the same town) and the child is usually older, doesn't have to be shuttled between schools (impossible, practically speaking) and wants to live with both parents equally (expressed through the attorney for the child).
You can certainly get better information sharing through a petition for modification/enforcement, and unless the pot or alcohol use is a major issue from a parenting perspective or is a true substance dependence/abuse, that kind of "gotcha" is not likely to be a big enough deal for CPS to investigate and recommend removal of the child (opiates, meth, selling drugs, maybe, pot and alcohol "use", eh, not so much, but simply one among many factors to be considered).
As to the support, it's hard to get to exactly 50:50 of all waking hours. Same as for tax deduction purposes, the parent that has the child 50.1% is the custodial parent. And even if you can get to 50:50, some support magistrates "deem" the parent who earns more as the "non-custodial parent" for the purposes of support obligations (that's what the case law actually suggests). However, other support magistrates and family court Judges will definitely cut the non-custodial parent some slack if it looks like exact 50:50 physical custody, or an attempt at same.
Threading all of these needles isn't too easy, however, and I'd confer with an attorney who can look at the last custody order and discuss it with you and propose various options and their probabilities of success.
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Unknown. To answer a probability question, we need to know whether you consented or not to your present order of support or not. The difference is enormous but I doubt you'll succeed either way.