Mostly no. Some words written without Polish characters can become ambiguous without context. For example: word "łaska" - "mercy", written without Polish lette

Mostly no. Some words written without Polish characters can become ambiguous without context. For example: word "łaska" - "mercy", written without Polish letter "ł" is "laska" - "stick". Although, in old good times some people used British pound character in texts to express this letter, since '£' is visually similar to 'Ł' and more often available. For other characters (ś,ź,ć,ż,ó,ą,ę) nothing like that was widely adopted. Workaround would be possible for 'ż' and 'ó' since they are (almost - see below) phonetically identical with 'rz' and 'u' respectively, but it wasn't popular, since most probably would be perceived as sign of very, very bad orthography. *Almost, since some people claim they can distinguish these, but it's not popular ability.