If the wood ends up strongest with 45% of the lignin removed I'd try to engineer a species with a lower lignin content to begin with. So-called 'weeping' variet

If the wood ends up strongest with 45% of the lignin removed I'd try to engineer a species with a lower lignin content to begin with. So-called 'weeping' varieties (Weeping Willow etc.) get their specific hanging shape from a later onset of cell wall hardening due to delayed lignin deposition so those might be a good start.