For example, ipa version of play is pleı and if l change it as plej in İPA. Are they stil pronounced the same ?
Yes, you can use [plej] instead of [pleɪ]; there's no significant difference. I've seen the diphthong /eɪ/ transcribed both ways in phonetic transcriptions: [eɪ] or [ej]. However, you cannot use [j] for interconsonantal [i], so [bit] or [bɪt] cannot be transcribed as *[bjt]. (The main difference between [i] and [j] is that the former is a vowel and has no constriction in the vocal tract, whereas the latter is a consonant, and thus has some amount of constriction in the vocal tract while articulating it.)
Also note that if precision is required, you'd use the non-syllabic form of [ɪ]: 'play' is transcribed as [pleɪ̯] in narrow transcriptions. ([ɪ̯] is actually the same as [j].)