Спасибо, так и сделал.
на всякий случай оставлю здесь содержимое модифицированного /usr/share/X11/xkb/symbols/ru - вдруг кому-то ещё пригодится, а то потратил несколько часов, пока разобрался...
// RUU (Russian-Ukrainian United keyboard layout).
// This is a modified Russian standard keyboard, with the third level containing
// Ukrainian and Belorusian alphabetic letters and commonly used Unicode symbols.
// For a description see http://wiki.opennet.ru/RUU [in Russian].
// ┌─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┲━━━━━━━━━┓
// │ ' ~ │ ! ≈ │ " ∞ │ № ₴ │ ; € │ % ‰ │ : ≤ │ ? ≥ │ * × │ ( { │ ) } │ _ – │ + ± ┃ ⌫ ┃
// │ ’ ́ │ 1 ÷ │ 2 ¤ │ 3 § │ 4 $ │ 5 ° │ 6 < │ 7 > │ 8 • │ 9 [ │ 0 ] │ - — │ = ≠ ┃Backspace┃
// ┢━━━━━┷━┱───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┺━┳━━━━━━━┫
// ┃ ┃ Й │ Ц │ У Ў │ К │ Е Ё │ Н │ Г Ґ │ Ш │ Щ │ З │ Х │ Ъ Ї ┃ Enter ┃
// ┃ Tab ↹ ┃ й │ ц │ у ў │ к ® │ е ё │ н │ г ґ │ ш │ щ │ з │ х │ ъ ї ┃ ⏎ ┃
// ┣━━━━━━━┻┱────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┴┬────┺┓ ┃
// ┃ Caps ┃ Ф │ Ы І │ В │ А │ П │ Р │ О │ Л │ Д │ Ж │ Э Є │ | ¦ ┃ ┃
// ┃ Lock ⇬ ┃ ф │ ы і │ в │ а │ п │ р │ о │ л │ д │ ж │ э є │ / \ ┃ ┃
// ┣━━━━━━━━┻━┱───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┬───┴─┲━━━┷━━━━━┻━━━━━━┫
// ┃ ┃ Я │ Ч │ С │ М │ И │ Т │ Ь │ Б „ │ Ю “ │ , … ┃ ┃
// ┃ Shift ⇧ ┃ я │ ч │ с © │ м │ и │ т ™ │ ь µ │ б « │ ю » │ . / ┃ Shift ⇧ ┃
// ┣━━━━━━━┳━━┻━━━━┳┷━━━━━┷┱────┴─────┴─────┴─────┴─────┴─────┴┲━━━━┷━━┳━━┻━━━━┳━━━━━━━┳━━━┛
// ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃
// ┃ Ctrl ┃ Meta ┃ Alt ┃ Space ┃AltGr ⇮┃ Menu ┃ Ctrl ┃
// ┗━━━━━━━┻━━━━━━━┻━━━━━━━┹───────────────────────────────────┺━━━━━━━┻━━━━━━━┻━━━━━━━┛
default partial alphanumeric_keys
xkb_symbols "ru" {
include "ru(common)"
name[Group1]= "Russian with Ukrainian-Belorussian layout";
key <TLDE> { [ U2019, apostrophe, U0301, asciitilde ] }; // Apostrophe and Stress symbol
key <AE01> { [ 1, exclam, division, U2248 ] }; // Division Sign and Almost Equal To
key <AE02> { [ 2, quotedbl, currency, infinity ] };
key <AE03> { [ 3, numerosign, section, U20B4 ] }; // Paragraph and Hryvnia sign
key <AE04> { [ 4, semicolon, dollar, EuroSign ] };
key <AE05> { [ 5, percent, degree, permille ] };
key <AE06> { [ 6, colon, less, lessthanequal ] };
key <AE07> { [ 7, question, greater, greaterthanequal ] };
key <AE08> { [ 8, asterisk,enfilledcircbullet,multiply ] };
key <AE09> { [ 9, parenleft, bracketleft, braceleft ] };
key <AE10> { [ 0, parenright, bracketright, braceright ] };
key <AE11> { [ minus, underscore, emdash, endash ] };
key <AE12> { [ equal, plus, notequal, plusminus ] };
key <AD03> { [ Cyrillic_u, Cyrillic_U, Byelorussian_shortu, Byelorussian_SHORTU ] };
key <AD04> { [ Cyrillic_ka, Cyrillic_KA, registered ] };
key <AD05> { [ Cyrillic_ie, Cyrillic_IE, Cyrillic_io, Cyrillic_IO ] };
key <AD07> { [ Cyrillic_ghe, Cyrillic_GHE, Ukrainian_ghe_with_upturn, Ukrainian_GHE_WITH_UPTURN ] };
key <AD10> { [ Cyrillic_ze, Cyrillic_ZE, paragraph ] };
key <AD12> { [ Cyrillic_hardsign, Cyrillic_HARDSIGN, Ukrainian_yi, Ukrainian_YI ] };
key <AC02> { [ Cyrillic_yeru, Cyrillic_YERU, Ukrainian_i, Ukrainian_I ] };
key <AC11> { [ Cyrillic_e, Cyrillic_E, Ukrainian_ie, Ukrainian_IE ] };
key <BKSL> { [ slash, bar, backslash, brokenbar ] };
key <AB03> { [ Cyrillic_es, Cyrillic_ES, copyright ] };
key <AB06> { [ Cyrillic_te, Cyrillic_TE, trademark ] };
key <AB07> { [ Cyrillic_softsign, Cyrillic_SOFTSIGN, mu ] };
key <AB08> { [ Cyrillic_be, Cyrillic_BE, guillemotleft, doublelowquotemark ] };
key <AB09> { [ Cyrillic_yu, Cyrillic_YU, guillemotright, leftdoublequotemark ] };
key <AB10> { [ period, comma, slash, ellipsis ] };
include "level3(ralt_switch)"
};
hidden partial alphanumeric_keys
xkb_symbols "common" {
key <AE01> { [ 1, exclam ] };
key <AE02> { [ 2, quotedbl ] };
key <AE03> { [ 3, numbersign ] };
key <AE04> { [ 4, asterisk ] };
key <AE05> { [ 5, colon ] };
key <AE06> { [ 6, comma ] };
key <AE07> { [ 7, period ] };
key <AE08> { [ 8, semicolon ] };
key <AE09> { [ 9, parenleft ] };
key <AE10> { [ 0, parenright ] };
key <AE11> { [ minus, underscore ] };
key <AE12> { [ equal, plus ] };
key <BKSL> { [ backslash, bar ] };
key <AB10> { [ slash, question ] };
key <LSGT> { [ slash, bar ] };
key <TLDE> { [ Cyrillic_io, Cyrillic_IO ] };
key <AD01> { [ Cyrillic_shorti, Cyrillic_SHORTI ] };
key <AD02> { [ Cyrillic_tse, Cyrillic_TSE ] };
key <AD03> { [ Cyrillic_u, Cyrillic_U ] };
key <AD04> { [ Cyrillic_ka, Cyrillic_KA ] };
key <AD05> { [ Cyrillic_ie, Cyrillic_IE ] };
key <AD06> { [ Cyrillic_en, Cyrillic_EN ] };
key <AD07> { [ Cyrillic_ghe, Cyrillic_GHE ] };
key <AD08> { [ Cyrillic_sha, Cyrillic_SHA ] };
key <AD09> { [ Cyrillic_shcha, Cyrillic_SHCHA ] };
key <AD10> { [ Cyrillic_ze, Cyrillic_ZE ] };
key <AD11> { [ Cyrillic_ha, Cyrillic_HA ] };
key <AD12> { [ Cyrillic_hardsign, Cyrillic_HARDSIGN ] };
key <AC01> { [ Cyrillic_ef, Cyrillic_EF ] };
key <AC02> { [ Cyrillic_yeru, Cyrillic_YERU ] };
key <AC03> { [ Cyrillic_ve, Cyrillic_VE ] };
key <AC04> { [ Cyrillic_a, Cyrillic_A ] };
key <AC05> { [ Cyrillic_pe, Cyrillic_PE ] };
key <AC06> { [ Cyrillic_er, Cyrillic_ER ] };
key <AC07> { [ Cyrillic_o, Cyrillic_O ] };
key <AC08> { [ Cyrillic_el, Cyrillic_EL ] };
key <AC09> { [ Cyrillic_de, Cyrillic_DE ] };
key <AC10> { [ Cyrillic_zhe, Cyrillic_ZHE ] };
key <AC11> { [ Cyrillic_e, Cyrillic_E ] };
key <AB01> { [ Cyrillic_ya, Cyrillic_YA ] };
key <AB02> { [ Cyrillic_che, Cyrillic_CHE ] };
key <AB03> { [ Cyrillic_es, Cyrillic_ES ] };
key <AB04> { [ Cyrillic_em, Cyrillic_EM ] };
key <AB05> { [ Cyrillic_i, Cyrillic_I ] };
key <AB06> { [ Cyrillic_te, Cyrillic_TE ] };
key <AB07> { [ Cyrillic_softsign, Cyrillic_SOFTSIGN ] };
key <AB08> { [ Cyrillic_be, Cyrillic_BE ] };
key <AB09> { [ Cyrillic_yu, Cyrillic_YU ] };
// include "kpdl(comma)" // uncomment this for comma instead of dot on numeric keypad
};