Substitution Cipher in Hangul

Japanese text can be written with some fifty kana, which can be enciphered with substitution ciphers. (Historical examples can be seen e.g., at 明治日本の暗号いろいろ). The Chinese language employs thousands of characters, so any practical encryption in Chinese is based on numerical code of those Chinese characters.

What about Korean? I have long wondered whether substitution cipher is possible in Korean script (Hangul). This is because Hangul text is not simply a series of Hangul letters. Instead, two or three Hangul letters (consonant+vowel or consonant+vowel+consonant) are combined to form a syllabic block, which is the unit of writing (morphemic block). Moreover, placement of letters within a block differs depending on the vowel. The vowels for A, E, I (which have a vertical axis) are written to the right of the initial consonant, but the vowels for O and U (which have a horizontal axis) are written under the initial consonant. So, simply substituting one Hungul letter for another may result in a letter sequence that cannot be formed into morphemic blocks.

Now, I learned possible simple solutions to my question. There may be two ways for substitution ciphers to work in Hangul.
(i) Substitution is applied in separate groups for consonants and vowels. This way, the "consonant-vowel" grouping is preserved in substitution. This is the approach that AI (Copilot) on my new PC gave to my question. Actually, AI at first gave an example of a Caesar cipher of consonants alone. When I asked about vowels, AI gave a separate substitution table for vowels. I do not know whether this simple scheme really works for actual Hangul text. (For example, I hear not every consonant can be the third element in a block; there are letters that are not simple vowels or consonants.) To my repeated requests to give actual examples, AI simply ignored "in Hangul" and gave websites for the Caesar cipher in Japanese!

(ii) Substitution is applied to morphemic blocks rather than to letters. Unicode registers 11,172 Hangul morphemic blocks (399 consisting of two leters + 10,773 consisting of three letters). If we think this whole set as a single alphabet, substitution cipher can be used. (An attempt to use the Vigenere cipher in Hangul (pdf in Indonesian?) seems to use this approach.)

Googling now finds applications to use cipher in Hangul, but I still cannot find actual examples of substitution ciphers in Hangul. Considering that Hangul was not used in official documents until 1894 and that I have seen use of numerical codes for telegraphy (posted here), substitution in Hangul may not have been common historically.