1) In Princeton is said about ид-у, идёшь -> идь-ошь and the change of quality in a consonant present in it : "Be happy to know that the change of hard consonant into soft produced, for example in this case, is completely general in the entire Russian verb system, all consonants capable of softening do so before endings beginning with {O}". I ask, putting apart cases like: irregular declensions of some pronouns (ты, теба), purely fictitious changes as consonant previously soft before an added soft consonant as well as particular behaviour of some consonants always soft/hard with every / some vowels and some other obvious case that I can't remember now; I ask, is present this change of quality of a consonant in other cases? Or it is only in present / future tense of verbs?
2) Is correct to say that in да(ва)ёшь, живёшь we are adding to the stems да(й)- and жив- two different endings: -йошь to the first verb and ь-ошь to the second? Since in да(й)ёшь й falls before any vowel or consonant because of its condition of a wimpy consonant. Thanks.