Technically yes for the physical install, but most counties require the work to be done by a licensed installer if the existing tank lid is being modified or replaced. Risers themselves are simple; the regulatory layer is the constraint.
More detail
Cincinnati and Northern Kentucky county HSTS regulations vary in their treatment of riser retrofits. Hamilton County Public Health treats riser installation as installer-licensed work when the existing concrete tank lid is being modified or when a new precast lid is being placed; a homeowner-installed riser without permit can trigger a re-inspection requirement at next sale and additional fees. Butler County General Health is similar. Warren County Health District and Clermont County Public Health treat simple risers (added on top of an existing intact lid) as less restrictive. Northern Kentucky Health Department has its own rules per Boone, Kenton, and Campbell county. Practical advice: call your county health department before any DIY riser work and ask whether the specific scope requires a licensed installer. If yes, the typical installer cost ($200 to $400) is much lower than the eventual re-inspection cost. The physical install is straightforward (excavate down to the existing lid, set the riser ring on the lid with butyl sealant, backfill around the riser, set the new flush-grade lid) and a competent homeowner with basic excavation tools can do it. The regulatory layer is what makes the DIY route risky from a compliance standpoint. One genuine DIY-friendly scenario: adding an inspection cap to the top of an existing riser that is already at or near grade. That is maintenance, not modification, and almost universally permit-exempt across Cincinnati metro and NKY.