Way to dynamically change content of presets built-in plugin in my nvim config?

[proofer]

Motivation: using LazyVim, and pursuant to an idea in Dusty Phillips's book, p. 101, I want to delete the presets M.motions mapping of ; so as to not have its group shown as Next ftFT. (And, for symmetry, omit the mapping of ,.) See below for context.

Is there a way to do this in my nvim config?

Context: my config currently contains this file:

-- mini-surround-flash.lua
-- Steal `;` from flash to use for mini-surround. Credit: Dusty Phillips.
-- In mini-surround, `;` replaces `gs` as prefix of the plugin's mappings,
-- and `;;` replaces `gsa` to add a surround.
-- In flash, the `;` forward repeat is omitted and, for symmetry the `,` back repeat is also.

return {
    {
        "echasnovski/mini.surround",
        opts = {
            mappings = {
                add = ";;",
                delete = ";d",
                find = ";f",
                find_left = ";F",
                highlight = ";h",
                replace = ";r",
                update_n_lines = ";n",
            },
        },
    },
    {
        "folke/flash.nvim",
        opts = {
            modes = {
                char = {
                    keys = { "f", "F", "t", "T" },
                },
            },
        },
    },
} 

[proofer]

Groups can be specified in the nvim config to override the one in the presets built-in plugin. So I added the following in the file shown in the OP:

    {
        'folke/which-key.nvim',
        opts = {
            spec = {
                -- override `presets` built-in plugin's group settings
                { ';', group = 'surround' },
                { ',', group = '' }, -- ',' is now a NOP and available for custom mappings
            },
        },
    },