Can the word is be a noun?

So I got bored in geography class and decided to make a sentence that makes no sense and goes along the lines of

"Is Muss isthmus? If Muss was isthmus, must he muss an if, if is, is thus?"

The only thing I really care about making this sentence grammatically correct is the "if" in "must he muss an if" and the "is" in "if is, is thus" Muss, meaning to mess up or untidy something, where as Muss first first used, is a person's name.

The "if" and "is" in question, can only be grammatically correct when a noun is used in it's place. So is "if" and "is" able to be used as a noun in this context or at all and can you actually muss an if?

Thank you in advance. - A very desperate high school student.

Anything can be a noun provided you put inverted commas around it, to indicate that its sense is in the word itself, rather than its active participation in the sentence, .

The "is" in your example, and in your title, should either be in quotation marks, or in italics.

Can the word is be a noun?

Only trivially: The seventh word in this sentence is is. The final is is a noun.

PS "isthmus" is a singular countable noun and requires a determiner