H2O2 are toxic for living things. as effect to H2O2 exposure, ROS (Reactive Oxygen Species) may be produced. Overproduction of ROS has lead to structural damage of protein, RNA and DNA, lipid peroxidation, etc.
I'm not sure that Hydrogen Peroxide can work as mutagen especially on seed. This chemical may be important on seed germination, but i'm not found any paper that report this chemical can induce mutation on seed. Mostly, Researcher use radiation and colchicine to induce mutation and polyplodization on seed.
If you're not sure. Why not performed your idea to use H2O2 as mutagen. If it's works, it Will be a greatest finding.