Lots of so called self confessed professionals will say to you that you ought to use certain entries in your Title, Description, alts, keywords and other places. Be sure that you have enough H1 and H2 tags and use bold a few times. Forget that! These worked very well years ago, but for Google in particular, these are more or less overlooked. I have successfully got web sites to the top of Google without even mentioning one or more of the search terms anywhere in the code.
I am not sure why people still insist on using these tags and attributes. From time to time, I think it is just to baffle less technical people. There might still be a small help in filing these attributes and tags with your desired keywords, but I doubt it is much. The difficulty is that they are too simple stuffed with random, irrelevant, keywords.
Search engines instead are putting loads of value in what happens off the website. So do not worry if changing your website code sounds too difficult or you do not maintain the code. You could do everything that is needed without changing a line of code!
Well, for my own web site design web site, I appear on the first page for various local listings, without mentioning the local areas on the site. As for instance, Merseyside does not appear in the code, yet I appear on the first page of Google for searches on site design Merseyside.
My home page does naturally discuss web site design and gives more details on the services offered. And this is the key to how a well optimised website page should look. The page should naturally mention and deal with the keywords. A few mentions of them, probably in different contexts and mentioning them in different ways. For example, website design and designing a web site.
Do not ever over-do the number of times that a keyword is mentioned in a website. Some people suggest a rule of each keyword representing no in excess of 2% of the words on a page. So, if the web page contains 300 words, which is a detailed page, then you could have no over 6 mentions of any of your individual keyword.
Take this to the extreme of a 200 word page, and if you used a keyword in the title, description, and keyword meta tags and once in an alt attribute, then you would have hit your 2% exclusive of mentioning it once in the text. So, for the finest results, be certain that that you declare keywords naturally instead of stuffing them everywhere that you might. But it is the next stage, link building, that is vital.