I just realized that there is no Guarantee Independence diplomatic action like in EU4 which is... concerning. There are historical examples of this in the nineteenth century, most important being the guarantee of neutrality for Belgium, Luxembourg, and Switzerland. In fact, the guarantee of Belgian neutrality via Treaty of London, 1839, played an important role in Britain's entry into World War I, as it was a signatory to that treaty as did Prussia, whose successor state German Empire violated it in invasion of Belgium.
Though, one issue with Guarantee Independence as a diplomatic action, as implemented in EU4, in application to treaties with respect to EU4 is that it could be easily revoked and almost instantly. I'm not sure if that would make any sense, though any countries could, by the nature of their own sovereignty, renounce or denounce a treaty that they had signed, though not always without consequences, especially the immediate kind.