What practical / halachic differences are there between mitzvos which are spelled out explicitly, and those stated generally e.g. ונשמרת מכל דבר רע, and תשבות, and ועשית הטוב והישר - which Chazal give specific applications? Please include sources/מראה מקומות
Although not practical right now, there is a difference in the fact that these mitzvohs that are explicit, the Tzedukim agree to them. In these instances, if Beis Din makes a mistake, they would not have to bring a korban as “every child knows it”. While any Mitzvah that requires Chazal to interpet, they would bring a korban if they made a mistake. This is mentioned in Horayus 4A
אמר רב יהודה אמר שמואל אין ב"ד חייבין עד שיורו בדבר שאין הצדוקין מודין בו אבל בדבר שהצדוקין מודין בו פטורין מאי טעמא זיל קרי בי רב הוא
§ Rav Yehuda says that Shmuel says: A court is not liable to bring an offering unless it issues an erroneous ruling concerning a matter with which the Sadducees do not agree. The Sadducees do not accept the Oral Torah, and they interpret the Written Torah literally. The court is liable only for a matter that is not explicitly written in the Torah or that does not clearly stem from that which is written in the Torah. But with regard to an erroneous ruling concerning a matter with which the Sadducees agree, the judges are exempt. What is the reasoning for this exemption? It is a topic that you could go learn in a children’s school. Since the matter the judges ruled upon is so obvious, their ruling simply exhibits ignorance, and is not deemed a ruling
It is also mentioned in a case of beis din mistakenly allowing someone to avoid the death penalty. Once they acquitted him, he cannot be returned to be retried. However if the mistake was something explicit in the Torah that the Tzedukim agree to, then he can be retried even after acquittal. This is brought in Sanhedrin 33B
ואין מחזירין לחובה: אמר ר' חייא בר אבא אמר רבי יוחנן והוא שטעה בדבר שאין הצדוקין מודין בו אבל טעה בדבר שהצדוקין מודין בו זיל קרי בי רב הוא
§ The mishna teaches concerning cases of capital law: But the court does not bring him back to be judged with a claim to find him liable. Rabbi Ḥiyya bar Abba says that Rabbi Yoḥanan says: And this is the halakha only in a case where the judge erred with regard to a matter for which the Sadducees do not admit to its validity, i.e., he erred in a matter learned from tradition or established by the Sages. But if the judge erred in a matter for which the Sadducees admit to its validity, i.e., a matter that is written explicitly in the Torah, it is a topic that you could go learn in a children’s school, and such an error negates the verdict and is reversed
An interesting question:
A specific mitzvah mentioned in the Torah would allow for many limmudim (exegesis). For example: Binyan Av etc... a general mitzvah either would not be possible or very difficult since it encompasses too much to argue a similarity to another mitzvah (though possibly it could generally be compared to other general mitzvahs).
I also don't know what is called general and specific. Presumably there is a delineation, but not placing a stumbling stone still can encompass a lot, though I presume this would be called specific.
תשבות mentioned many times comes to include or exclude a day to be similar to Shabbos or Yom Tov. Interestingly the Ramban on Parshas Emor (Vayikra 23:24) explains that there is a general rule to rest on shabbos (שבות), and the sages decided what is considered rest and what is not. This would include for example doing business on Shabbos (according to the Ramban a Torah law, though not equivalent to מלאכה, prohibited work). Also see Ritva 16a (ד׳׳ה ותניא ר׳׳ע). And so presumably any general law might have much more leeway given by Hashem to the sages in how it may be understood and applied.
A specific mitzvah can also be time bound and exclude many people, but a general will not (once again this depends on your delineation where a law is not general and specific and so the statement might only be true by definition then).
There is a גמרא in ביצה ל עמוד א and also in שבת קמח עמוד ב that deals with a concept מוטב שיהיו שוגגין ואל יהיה מזידין, that we say if there are those doing something wrong, one shouldn't protest and inform them of the prohibition so that they will not intentionally violate the prohibition (of course this is where we don't assume that they will listen עי' תוספות שבת נה עמוד א). The רא"ש in ביצה פ"ד סימן ב quotes from the בעל העיטור that this is only said on what isn't explicit in a verse, but what is explicit in a verse you must protest without regarding that it may cause intentional violation of a prohibition. This is codified by the רמ"א in שלחן ערוך אורח חיים סימן תר"ח סעיף, ב בהגה.
There is a משנה למלך פי"ג מהלכות שגגות ה"ה בא"ד ד"ה אמנם, that is a very long piece, but in the middle seems to say דכל שאינו מפורש בתורה אין עונשין עליו, whatever is not explicit in the Torah that we don't give punishment on it.
The פתיחה כוללת of the פרי מגדים in חלק ראשון may be of interest.