RDA 22.214.171.124.2 covers minor changes to the title proper. Minor changes in AACR2 were under 21.2A2; there are only minor differences in wording)
a) a difference in the representation of a word or words anywhere in the title (e.g., one spelling vs. another; abbreviated word or sign or symbol vs. spelled-out form; arabic numeral(s) vs. roman numeral(s); numbers or dates vs. spelled-out form; hyphenated words vs. unhyphenated words; one-word compounds vs. two-word compounds, whether hyphenated or not; an acronym or initialism vs. full form; or a change in grammatical form (e.g., singular vs. plural))
LC-PCC PS 126.96.36.199.2 Category A (formerly LCRI 21.2A2). "Consider that "one spelling vs. another" applies both in the case of ordinary orthographic variations and in the case of official orthographic changes. Consider that "a change in grammatical form" includes singular vs. plural, adjective vs. noun, and genitive vs. nominative case."
b) the addition, deletion, or change of articles, prepositions, or conjunctions anywhere in the title
c) a difference involving the name of the same corporate body and elements of its hierarchy or their grammatical connection anywhere in the title (e.g., the addition, deletion, or rearrangement of the name of the same corporate body or the substitution of a variant form
LC-PCC PS 188.8.131.52. Category C. "If the change is in the name of a body that is part of the title proper and the change requires the creation of a new heading for the body (see RDA 184.108.40.206), consider such a change to be a major change. Consider the presence or absence of the name or title of the official of the body to be a minor change. Consider the presence or absence of the body to whom a publication is presented to be a minor change."
d) the addition, deletion, or change of punctuation, including initialisms and letters with separating punctuation vs. those without separating punctuation, anywhere in the title
e) a different order of titles when the title is given in more than one language in the chief source of information, provided that the title chosen as title proper still appears as a parallel title
LC-PCC PS 220.127.116.11. Category E. "Also apply this category when the title is given in more than one script. Do not consider there to be a major change even if the addition of the title in another language or script on a later issue would affect the choice of title proper if the description were based on that issue. However, consider that there has been a major change if there is evidence that the publisher intentionally changed the title; such evidence may include, for example, a statement by the publisher or a new ISSN printed on the publication."
f) the addition, deletion, or change of words anywhere in the title that link the title to the numbering
g) two or more titles proper used on different issues of a serial according to a regular pattern
LC-PCC PS 18.104.22.168. Category G. "Also apply this category when the language of the title varies according to the language of the text. However, consider that there has been a major change if there is evidence that the publisher intentionally changed the title; such evidence may include, for example, a statement by the publisher or a new ISSN printed on the publication."
h) the addition to, deletion from, or change in the order of words in a list anywhere in a title, provided that there is no significant change in the subject matter
LC-PCC PS 22.214.171.124. Category H.: "Consider that "a list" means at least three terms."
i) the addition, deletion, or rearrangement anywhere in the title of words that indicate the type of resource such as "magazine," "journal," or "newsletter" or their equivalent in other languages. ["rearrangement" was formerly only in the LCRI; it is now part of the rules]
LC-PCC PS 126.96.36.199. Category I. "The change from one word to another (e.g., the change from "magazine" to "journal") is a major change. The word "series" does indicate a type of resource. A word denoting frequency (e.g., "monthly") does not indicate a type of resource."
RDA 188.8.131.52.2 (last sentence): In case of doubt, consider the change to be a minor change.