No one is forced to change plans due to a change in eligibility for Marketplace subsidies. However, if you are enrolled in a Marketplace plan, your annual household income has changed, and you now earn more than 250 percent of the federal poverty level (which is the income limit to qualify for cost-sharing reduction subsidies, or CSRs), you are entitled to a special enrollment period to change plans.
If you are enrolled in a silver plan and lose eligibility for CSRs, you may change to a plan one metal level above or below your current plan, but you are not required to do so. If you choose to stay in a silver plan (but with different cost-sharing, appropriate to your income), then any out-of-pocket costs you already paid during that year must be counted against the out-of-pocket costs required under the new version of the plan. (45 C.F.R. § 155.420(a)(4)(ii)(B)).