Scope of Practice questions should be referred to--yup, your state nursing board "Scope of Practice." Each state has its own. If after reading it you are still confused write to the BON and ask. Even if they don't answer directly they will put you in touch with someone who can.
This being said, I find it doubtful that you'll find much in the SOP because the question is too specialized to Occ Health Nursing.
As an RN you should have a relationship with a Medical Director which might be an MD, or if allowed a ANP or PA. If you do not have such a relationship in your company which might be the case, well this would make me cringe as you need Standing Orders even to give aspirin in the case of a suspect heart attack as well as Tetanus Immunizations, oxygen, etc. I would not work for a company without such a line of command though the strength and ease of the connection varies. I've worked where I have a MD (Medical Director, who is an MD) available at all times and have worked where I theoretically had one available (but getting a response was difficult).
To turn back to restrictions. I've (following protocols handed down to me) have been able to create restrictions for 24 hours and could extend them for good reason (inability for the EE to see a Practitioner) and have always felt comfortable with that. Restrictions like "no push/pull" or "no lift more than 5lbs" or "no work more than 8 hours for the day," as well as "you're out'a here right now." (That's a CYA move when I have an EE who is not taking an issue as seriously as I want him/her to do). I'd generally (at most places) follow that up with a call or note to the covering Practitioner explaining what and why I've done what I've done, and I've never been called back to change such a short term set of restrictions. But as for creating modified/light duty work specs for more than a day I'll say right out "no way."
As Aarakoto pointed out creating restrictions can create recordables though prophylactic same day restrictions is not medical treatment and does not. Create work restrictions for a longer period of time may create a recordable and in my opinion is not w/in your realm.
Often I'd have a form connected to that company that listed what that EE did on what job, a "Job Analysis" it had a series of questions from "does EE drive," to "lift 0-5lb," "5-10lb," etc. It included climbing, running, kneeling, and had check-off spaces for "never," "occasionally," "frequently," etc. With the EE and the Supervisor (if needed) I'd utilize this tool and give the EE a copy of it to take with him/her to see their Practitioner with a request that specific restrictions or limits be returned. Often with the EE's permission I'd communicate with the Practitioner as to enable that person to see the complete picture.
The EE is often (but not always) the best source of what to do for temporary restrictions and if I thought a worker could lift 0-5lbs but the worker said: "no." Well, that's a warning to go up the chain, even if the worker is a slacker--there is too much risk to do otherwise. I've always found most workers quite willing to be vocal about what they can do and can't do. True abusers/slackers are rare, but they do occur and can be a pain--though be careful for someone who is clearly abusing the system may have other reasons that need to be teased out that in fact point to medical necessity such as panic/anxiety attacks.
Very short term restrictions are generally accepted with good reasoning and documentation and with a required "do not come back until you have a Practitioner's ok unrestricted or with restrictions. But document well and be conservative and if in doubt--don't. Just my thoughts--good luck.